OPT

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Observation Preparation Tool (OPT)

1. An Overview of the Observation Preparation Tool Web Application

1.1. Introduction

Abstract

This document describes the web-based tool to create Scheduling Blocks (SBs): machine readable instructions for radio astronomical observations using the Karl G. Jansky Very Large Array (VLA) and its WIDAR correlator.

This Observation Preparation Tool web application (OPT web application) consists of three separate tools that are used in conjunction. These are the Source Catalog Tool (SCT) to define and select positions in the sky, the instrument Resource Catalog Tool (RCT) to define and select hardware (receiver and correlator) settings, and the Observation Preparation Tool (OPT) to define and create a sequence of scans where a scan is a combination of an observing mode, a source, a resource, a time interval, and a scan intent.

This manual guides the reader through the three tools, providing adequate information and scheduling hints to create an observing schedule for observations with the VLA and how to submit the schedule to VLA operations. Considerable observing details and suggestions are collected in the VLA Guide To Observing. Additional specific guidance can be obtained through the NRAO Helpdesk.

The VLA will be observing in a mode where the observing schedule to be executed is selected from a pool of valid schedules just before the actual observations take place. This Dynamic scheduling is described in the VLA Guide To Observing. The life-cycle of the SB, some practical considerations for a higher success rate in the observing pool and, e.g., more detailed instructions for performing line observations that depend on Doppler calculations can be found there.

The Observation Preparation Tool web application (OPT) is a product of the National Radio Astronomy Observatory staff. The Karl G. Jansky Very Large Array (VLA) is operated by the National Radio Astronomy Observatory (NRAO), which is a facility of the National Science Foundation (NSF) operated under cooperative agreement by Associated Universities, Inc. (AUI).

 

Purpose of this Document

The purpose of this document is to provide help to the individual preparing VLA observations with the WIDAR correlator. This document consists of an introduction to the Observation Preparation Tool (OPT) web application, hints and preliminary "cookbook"-like approaches to create a successful observing schedule. This document is not suited to learn, nor intended to teach, observing strategies and good observing practices. The Observational Status SummaryVLA Guide To Observing, and other VLA documentation are great resources with further references. For more specific questions one may consult the NRAO Helpdesk.

An observing schedule using the VLA receivers, electronics and correlator is made through the OPT web application. It consists of a description of an observing run: a Scheduling Block (SB) that is made up of a sequence of observing scans. To make full use of the OPT, it may be necessary to predefine (enter) sources to be observed using the Source Catalog Tool ( SCT), and to possibly predefine the frequency and correlator settings to be used using the hardware and instrument configuration Resource Catalog Tool (RCT). This document should aid in creating source and resource lists, and creating the final observing schedule (an SB). Alternatively, if no user catalogs are defined, one can resort to observing known (calibrator) sources using standard correlator settings, although using these catalogs only may be rather restrictive in scientific discovery space.

 

Abbreviations Used in this Document

The OPT, SCT and RCT abbreviations were introduced in the previous section.  When referring to the OPT in the remainder of this document, it is implicitly referring to the tool that creates a sequence of observing scans. On the other hand, when we refer to the OPT web application we specifically refer to the combination of tools consisting of OPT, SCT, and RCT.

The use of the term '(re)source' is short-hand for the text "source and resource": the sentence applies to both source and resource. Similarly, using 'project (etc.)' allows us to avoid having to write "project, program block(s), scheduling block(s), and scan(s)" which otherwise would make sentences confusing. For program block and scheduling block we will use PB and SB, respectively, or blocks when we mean either or both.

We will further use PST (Proposal Submission Tool) and TAC (Time Allocation Committee), which have some interaction or influence on what goes on in the OPT web application.

1.2. The Observation Preparation Tool Web Application

The OPT Web Application

The OPT web application is started by pointing your web browser to https://my.nrao.edu/ (note the extra s in https for encrypted connection). It will require you to log in to the NRAO user data base, for which you probably already registered as otherwise you would not have been able to submit the proposal. If necessary, (re)register with an email address known to NRAO, e.g., if you are a co-investigator who did not submit the proposal. Do not use the registration owned by someone else as this will severely upset the system.

After logging in to the NRAO user data base, click on the Obs Prep menu tab at the top.

This will redirect you to a welcoming page containing a link to the OPT web application. In the OPT web application, you will notice the top two blue horizontal strips, one menu strip labeled File, Edit, Views and Help, and a navigation strip: NRAO > User Portal > .. and Exit. The web application opens up in the OPT (i.e., the scan sequence tool, in the navigation strip labeled as Observation Preparation), but also lets you navigate to the SCT and RCT (in the navigation strip using the links labeled Sources and Instrument Configurations, respectively). We have tried to keep the OPT, RCT and SCT tools as well as, e.g., editing concepts as similar as possible so that the look and feel in one tool should be similar to that of the other.

Note that the OPT is a web application using JAVA. It should thus be available and perform similarly on most common web browsers and operating platforms. By using JAVA,  the big advantage is that we can keep everybody up to date with the latest code without having to worry about the hardware and software you use. A drawback is that it may take a while to connect and reconnect between user web browser and NRAO user data base, i.e., that operations may take longer than expected. Also, the web application has to time out at a certain point, and connections may be interrupted unexpectedly and/or inconveniently. To exit gracefully, go to File in the menu strip and choose Exit (which is typeset as FILE - EXIT from here), or find the Exit button at the right hand side of the navigation strip.

Do not use the browser back button to navigate to the previous page. This may give browser errors that might prevent you from working on your project for a few hours. Also, please be patient; when you enter or click something it may take a few seconds to connect back and forth between your browser and the NRAO data base. You want to avoid clicking or entering before the previous action was completed. Be patient and watch the busy icon of your browser to cease (and sometimes even a bit longer). If you continue to have problems, contact us through the NRAO Helpdesk.

 

The OPT, SCT, and RCT Tools

The Observation Preparation Tool (OPT) is one of the three tools (OPT, and SCT and RCT) of the OPT web application, and is used to schedule an observation by creating a list of scans and to generate an observing run (Scheduling Block) from that list. Each scan consists of a telescope pointing direction (selected from the SCT below) using a specific hardware and instrument configuration (selected from the RCT) combined with an observing mode action lasting for a time interval (specified using this OPT), and typically for a specific reason, an intent. A schematic flow diagram with these components is shown in Figure 1.1.

Figure 1.1: Schematic flow diagram from an approved proposal to completion of all observations for a project. The purpose of the Observation Preparation Tool web application is to get from the proposal to the observing scripts. Flow along the gray arrows is the responsibility of NRAO. Either NRAO or the user will have to fill out the path along the flow of the white arrow. The flow along the black arrows is the responsibility of the user, using the SCT (blue box), the RCT (red box) and the OPT (green area) in the NRAO OPT web application. The source list supplied in the PST will be transferred to the SCT for approved proposals; in the future this will happen for non-standard resources supplied in the PST as well but for now they have to be created in the RCT by the user.

The Source Catalog Tool (SCT) is the OPT web application tool that is used to specify a collection of telescope pointing directions, from which one can select when creating a list of scans in the OPT.

The Resource Catalog Tool (RCT) is the OPT web application tool that is used to specify a collection of hardware and instrument configurations, from which one can select when creating a list of scans in the OPT.

 

Projects, Program Blocks, & Scheduling Blocks

A project (an orange P: Project; Figure 1.2) consists of at least one program block (PB, a blue PB: Program Block), which is defined as a collection of observations for a single proposal using a single VLA array configuration. That is, typically a PB does not extend to another allocation semester; e.g., if you were allocated time for the A array and the B array, one PB would be defined for the A array and one would be reserved for the B array observations, perhaps in a following semester. You may also find PBs for the same array configuration but with time allocations split over different scheduling priorities. A PB is made up of at least one scheduling block (SB, a green SB: Scheduling Block), which consists of a sequence of scans (a radio telescope: Radio Telescope): combinations of a timed telescope pointing direction (a source) using a specific hardware and instrument configuration (a resource) in a specified observation mode with a specific intent. Scans may be grouped in scan loops (a looping circle: Scan Loop), or loops (of loops, ..) of scan loops.

For fixed date observing, each allocated time slot will typically be equivalent to an SB. For dynamically allocated observing time, an SB is not necessarily the same as a complete observation; a complete observation is when all data on the target(s) has been obtained. This may be a single SB or a random or specific order of several executions of SBs on the sources of interest, whether or not on the same observing day, possibly interspersed with an SB performing flux calibrations, an SB performing observations at a different frequency, etc.

OPT Figure 1.2

Figure 1.2: The project (P) tree consists of at least one program block (PB); A PB is made up of at least one scheduling block (SB), which consists of a sequence of scans with or without loops of scans.

In general, SBs may be many different snippets of an observing run, i.e., groups of consecutive scans that constitute a complete observation (a PB), but an observing run may as well be defined in a single SB. It depends on what the user finds convenient and what is smart given the scheduling priority; for example one can define a template SB containing the scans when starting with the flux density calibrator J1331+3030 (3C286) that can be copied to each new PB assigned by the TAC.

 

Page Layout of the OPT Tools

The front page of the Observation Preparation Tool (OPT) is is the page shown directly after redirection by the NRAO user database. The front page shown after navigating to the SCT or RCT is very similar. The web browser window is set up in four main panels (Figure 1.3):

  • The menu and navigation strips at the top
  • The interface feedback strip at the bottom
  • The left hand side column; in the OPT it contains a collection of projects, in the SCT it contains a source search section and a collection of source catalogs, and in the RCT it contains a collection of resource catalogs (hardware/instrument settings).
  • The main editing window; a project (etc.), source or resource manipulation field where most of the editing for each of the different tools occurs.

Figure 1.3: General layout of the OPT web application page in the web browser. For the SCT, the left hand side column includes a source search tool and thus looks slightly different (see inset left).

The menu and navigation strips are the first and second line, respectively, at the top of the web interface with menu/navigation items written in white letters on a dark blue background.

The menu strip is used to manipulate – import/export, create/edit, cut/paste – projects (etc.) and (re)sources. The navigation strip allows one to switch between the three components (OPT, SCT, and RCT) of the scheduling software; the bold-faced name is the currently active tool and the underlined names are links to the other tools.  Note that we use Observation Preparation for the OPT, Sources for the SCT and Instrument Configurations for the RCT.

More on using the menu items can be found in later chapters.

Occasionally you may encounter the reddish colored Important message banner just below the menu and navigation strips.  We use this banner to convey anticipated downtime, emergency software updates, etc., suggesting you to postpone or finish your work promptly.

The interface feedback strip is the strip over the full web page width at the bottom of the page. This strip is used to display feedback information such as error messages (red font) and warning messages (blue font) generated when entries made through the web interface are validated. It is advised to pay attention to these messages as it may be the only indication that a schedule is faulty. Blank warning messages and some messages at the beginning of an SB (pertaining to on-source time of setup scans) can be ignored. An SB with errors cannot be submitted, but a SB with warnings may be submitted if the observer persists. Please note that the interface feedback strip may include a scroll bar when there are more warnings and errors to display than fit directly on the visible part of the pane.

The left hand side column, depending on which tool is selected (OPT, SCT or RCT with their more descriptive names in the navigation strip), should have at least one project, source catalog or resource catalog visible.

  • OPT (Observation Preparation).  The OPT project column should contain the program for which you were awarded observing time. If not, please let us know as soon as possible using the NRAO Helpdesk. Other catalogs may be visible, in particular if you had previous observing programs or if you were awarded observing time for more than one project in this proposal round. Different icons in the tree depict different items: Project for projects, Program Block for program blocks, Scheduling Block for scheduling blocks, and Radio Telescope for scans or Scan Loop for scan loops.  When using this for the first time, it may only show the Project; a project tree would be visible all the way to the first scan level with consecutive mouse clicks on the item names in the tree. Some of the information may have been entered from the details of your proposal and should be read-only.

    A small plus-sign (xpnd) icon in front of a project or catalog means that there are items defined within that item; click on it to expand and display a tree-view of these items. For example, clicking on a plus-sign icon in front of a project ( Project, orange P) will expose, or expand, a list of PBs in that project, etc. Clicking a small minus-sign (clps) icon will hide, or collapse, all content within that item. For speed and memory reasons, not all projects are loaded into memory from the start; if there is no plus-sign associated with the project or SB you would like to work on, simply click the project name to load it in memory.

    At the top of the left hand side window, there is an icon menu. These icons can be clicked to cut/delete or copy/paste entire PBs, specific SBs, individual scans, (re)source catalogs, or (re)source groups. The options of this icon menu act only on the items in the tree, not on the items in the main editing window. In contrast to the small icons in front of a tree item, plus-sign and minus-sign icons in the icon menu expand or collapse the tree under a selected (highlighted) item. Arrow icons move items around in a tree. Navigating between projects, blocks, and scans in the OPT is simply done by selecting (click to highlight) any such item name in the tree. Similarly, one can navigate between a tool’s catalogs and groups in the left hand side column trees (in SCT and RCT).

  • SCT (Sources)  At the top of the left hand side column of the SCT, below the icon menu, is an interface to search for sources. The source search is performed on a source name only in the selected source catalog (highlight it by clicking) in the list of catalogs in the bottom part. Alternatively, the source is looked up in the SIMBAD data base when the external search field and button are used. Check the alias box if you have not entered the name of the source in the selected catalog but, e.g., its 3C name. Use Advanced Search if you want to search on something else than a source name in a single catalog, e.g., using a cone search on a position with a flux density limit.

    In the bottom part of the left hand side column of the SCT, there should be at least one source catalog visible in red italics, namely source catalog VLA, containing the VLA calibrator list. There may be other source catalogs visible, e.g., catalogs that you have defined yourself. Catalogs in red italics are read-only. Small plus-sign icons mean that there are groups of sources defined within a catalog; click on it to expand and display these groups. The VLA catalog also contains subgroups that can be expanded.

  • RCT (Instrument Configurations)  At least one resource catalog is visible in the RCT resource catalog column, in red italics, namely resource catalog NRAO Defaults. It currently contains the NRAO default hardware/instrument settings for wide band (continuum) and spectra-polarimetry per observing band. Furthermore it contains WIDAR setups for pointing scans for observing at the higher frequencies. Other resource catalogs may be visible, i.e., if any were previously defined. The same editing and navigation rules apply as for SCT catalogs, e.g., catalogs in red italics are read-only.

More on manipulating PBs, SBs and scans in the OPT, manipulating (re)source catalogs and (re)source groups, and using the source search tool can be found in later chapters.

The main editing window, or manipulation field, exposes different information fields per tool and per item type. However, the SCT and RCT in first instance both show a very similar table of catalog contents, i.e., a table of entries in the selected catalog or group. First we describe the OPT case as it is the first you will see when logging in to the OPT web application.

  • OPT When a project is selected (highlighted), the main project manipulation field will show the details of this project (and PB, SB or scan details on underlying levels). Most of this upper level information has been transferred from the PST or entered by NRAO staff, in particular the total allocated observing time. Investigators not on the original proposal but involved in the observing or data reduction can be added to the project here at any time. The information in this OPT window will be different according to the item that is selected. If a PB is highlighted, information on array configuration  and underlying SBs appear, with the time allocated to that PB. When SBs are executed, the execution block table summarizes the dynamic scheduling starting conditions. The information on selecting a SB is spread over four pages, each accessible via its own tab at the top of the main window: Information (with SB name, count, LST start range and conditions), Reports (with resource, source and scan summary listings), Validate & Submit and Executions. There is also a Bulk Scan Edit tab that will be explained later. Selecting a scan deploys another couple of tabs in the main editing window.
  • SCT Selecting a source catalog or group within a source catalog in the SCT will show the sources in this catalog or group in the form of a table listing in the main source manipulation field. If the list contains more than 25 sources, this list will occupy multiple pages, which can be browsed using the page selection buttons at the top and bottom of this table in the main window. Instead of 25, one can select a higher number of entries per page at the top of the table. The source table contains a source per row with a check box, an editing icon (Edit Source), a field for the source name, the coordinates and other details. The coordinate frame used for display in the table is listed above the source table, and may be re-selected. Hovering the mouse over the items in the Details or Aliases column pops up additional source information when available. Finally, clicking on the Sky Map icon opens a new browser tab with detailed information on the sky and VLA calibrator sources surrounding up to ten degrees around the position of that source.
  • RCT A selected resource catalog or group within a resource catalog shows a similar table listing in the main resource manipulation field, but now with resources. Again, initially there are up to 25 entries per table (i.e., per page) shown, and the different pages are navigable using the buttons at the bottom. The resource list contains a resource per row with a check box, an editing icon, a field for the resource name, frequency band, visibility integration time, AC/BD bandwidth, AC/BD center frequencies, back-end of the resource, and a field for user comments.

More on manipulating block and scan information, or on manipulating (re)source information can be found in later chapters.

1.3. Before You Begin

Guidelines

The following guidelines, in somewhat preferred order, allow to avoid the most obvious problems and in general is a good way to proceed. Also, we have set up this manual to make you familiar with the tools, features, possibilities, concepts and practicalities in a relatively natural way, so that a next step becomes almost intuitive.

  1. Collect proposal information to remind yourself the details of your observing proposal. It is good to have your proposal handy; it should be available in the PST if you do have a printed copy already. You will need the positions of your target sources and calibrator sources for flux density, delay/bandpass and gain calibration. Resource information for wide band continuum observations includes the frequency bands of your observation. For spectral line observations you need either an exact sky frequency or a combination of rest frequency, velocity and velocity reference frame information on your target sources, and the details of the correlator configuration.
  2. Check the project, in the OPT labeled with the project code, in terms of program/scheduling blocks entered by NRAO staff. This read-only information will likely be the project name, PB and allocated time, array array configurations, and scheduling priorities. Source catalogs will be created with the PST information provided but make sure that the positions are transferred correctly and to sufficient accuracy for your science. Resource catalogs will have been made but be left empty at this stage. The NRAO Helpdesk is available to clarify any confusions.

 

After Logging into the OPT Web Application

Projects do not appear in the OPT directly after the disposition letters are sent. They are created a few months later, about a month before the reconfiguration to the first possible array configuration of the observations. The page shown directly after logging in to the OPT web application should be the OPT front page with your project tree consisting of a PB and an (empty) SB. Some information on this page should be already filled out and read-only. Check this information with the information you gathered in the previous section and inform us as soon as possible if you think there is an error in any of these fields; the sooner you check this the sooner we can have it corrected, and the sooner you can start creating SBs. Fortunately, it most likely won’t be that complicated, but it is a good idea to allow yourself ample time to get used to the tools and to let us help you with your questions.

The remainder of this document will guide you through the different components to create an SB/observing schedule. The SCT is the easiest and most logical to start with. The RCT and OPT use many features or concepts that are similar to the features or concepts in the SCT and thus need not be addressed again. As the OPT must use information defined both in the SCT and in the RCT, a chapter on the RCT is placed before the chapter on the OPT.

If at any time you wish to exit, use FILE - EXIT or the Exit button on the top right hand side of any of the tools. Please do not exit the tool by closing the web browser or browser tab before exiting properly, with either of the exit options, as this will keep your session alive and will create problems accessing (read: approving) your SB for some hours.

As an advance hint on user friendliness, experience has shown that it is convenient to keep the RCT and SCT catalogs or groups as compact as possible because you need to select from these catalogs in the OPT. That is, it is best to keep only the sources and resources you want to use in a single observation in a catalog and to include the calibrators from large lists (e.g. the VLA calibrator list) already in that source catalog, with perhaps a different, more descriptive name. What is meant by this and why will become clear later on.

 

    1.4. Suggestions, Help, and Contact

    The remainder of this document concentrates on a hands-on cookbook-like detailed description of the OPT, SCT and RCT.  If you find yourself stuck and need help with the tools, if you have excessive problems with web interface issues, or if you just need some hints or pointers for optimal user convenience, we can be contacted through the NRAO Helpdesk.

    As much of this information may be new to you, please do not wait until the last moment to schedule your observations!

    The same holds when asking for help. If possible, we suggest that you start at least two weeks before your planned observations, allowing enough time to address any scheduling problems or other issues.

    2. Working with Catalogs in the OPT and Using the Source Catalog Tool (SCT)

    2.1. Orientation and Working with Catalogs in the OPT

    Log in to the OPT web application and, assuming that there is no message in the Important message banner that makes you decide to abandon the OPT for the moment, look for the navigation strip at the top. If Sources is not in bold face, but in normal font and underlined, click it with your mouse button to navigate to the SCT (Figure 2.1). To exit the tool properly, use the Exit link in the upper right corner or log out with FILE - EXIT; do not kill the browser window/tab!

    A short introduction to the layout of this tool's page has been given in the introduction (Chapter 1). There is an icon menu at the top and a source search tool below it in the left hand side column. At least one VLA catalog must be visible in the bottom part in the left hand side column, which is the catalog browser (Figure 2.1). For orientation and to get a feel for the tool(s), it is instructive to walk through this VLA catalog first. The search tool will also be described. After this orientation it should be almost intuitive to create your own personal source catalog(s) which you will use in your project's SB scans. Note that a source catalog for each of your successful proposals may be pre-filled; it is important that you check the pre-filled information for correctness.

    Figure 2.1: Web browser screen shot of the SCT page showing the first few sources in the DEC=-10 group, which is part of the Dec Groups in the read-only VLA catalog of sources.

     

    Example of a Source Catalog: the VLA Calibrator Catalog

    The VLA catalog (Figure 2.1) is the VLA calibrator list, described in the VLA calibrator manual. These sources are suggested to be good calibrators for specific frequencies and array configurations, but not necessarily for all frequencies in all configurations. Browsing this source catalog is instructive to become familiar with catalogs in the OPT web application and with the information available for sources. The source search tool is an extra feature in the SCT only.

    Note that the VLA source catalog is in red italics, which means that this catalog is read-only.  A plus-icon (xpnd) in front of the open book icon (Open Book) indicates that a catalog includes source groups. A catalog does not need to contain groups, but at some point it may be more convenient to create them. If you click the plus-icon or VLA (or, in general, the name of the catalog) these groups will appear in the catalog tree and the plus-icon will change to a minus-icon (clps).

    If you click on the catalog name, here VLA, you will also see the contents of the highlighted VLA catalog in the main SCT window, the big field to the right hand side of the catalog column (Figure 2.1). This table list combines the contents of all groups and possible entries in the catalog that do not belong to a group (though in this case there are no such free-agent entries). The pre-defined groups in the VLA catalog are RA Groups, Dec Groups, and VLA Flux Cal. The RA Groups and Dec Groups also have subgroups (Figure 2.1), but these subgroups are a special case implementation in the VLA catalog only; groups cannot be nested.  When a group name is highlighted (or selected) using the mouse button, the right-hand side window with the contents will only show (filter) the sources which were grouped in this sub-catalog. For example, selecting the VLA Flux Cal group will now only list the standard flux density calibrator sources. Similarly, the DEC +10 subgroup will show the VLA sources with Declinations between +10 and +20.

    Clicking VLA differs from clicking the plus-icon in that it will expose the total content of the catalog in the main (editing) window, with 25 sources per page, starting with source J0001+1914 (clicking the plus-icon only exposes the names of the groups in the left hand side column). At the top of the table, you will notice that the top line is a small page navigation menu. A similar page navigation menu can be found at the bottom. This VLA catalog contains more entries that fit on the page (25), and in this case is distributed over many pages. Below is a list of the menu icon buttons and what they mean:

    Arrow First first page of the catalog (or group)
    Arrow FR 10 pages backward in the catalog (or group), or as many as possible if less than 10 exist
    Arrow Previous previous page in the catalog (or group)
    1, 2, .. individual page numbers in the catalog (or group), with the current page highlighted
    click to select another page from this small list (up to ten page numbers) if desired
    Arrow Next next page in the catalog (or group)
    Arrow FF 10 pages forward in the catalog (or group), or as many as possible if less than 10 remain
    Arrow Last last page of the catalog (or group).

    If you find the default of 25 lines per table page too few, you can change to a larger number of lines per page (50, 100 or 200) at the top of the page.  Every table column with the font turning orange when the mouse hovers over it can be sorted by using a click of the mouse button.  All pages in the catalog are used in the sorting which means that catalog entries may have moved from one page to another after a sort. When a column is sorted, it will show a small orange arrow next to the header name, pointing up if the column is sorted in ascending order (going to larger values when going down in the table) and pointing down when the sorting is in descending order. A sorted table can be re-sorted in the opposite direction by clicking the column again (note that the header of a sorted column, the one with the arrow, might not change to the orange color anymore).

    As a small exercise, use the navigation tools at the top or bottom to confirm that (with 25 sources per page) the catalog has 75 pages. Using the table header sort, confirm that the source with the most southern Declination is J1118-4634.  For any source, hovering over details or aliases pops up additional information on the sources if available: flux densities at different frequency bands, closure phase properties and aliases for the source in non-sortable columns (see the key to the VLA calibrator manual). The angular view near a calibrator on the sky can be displayed in a new browser tab by clicking the Sky Map icon (bullseye). Above the table on top of the page, it is shown that the coordinates in the table are in the Equatorial coordinate system. If another coordinate system is selected in the drop-down menu, e.g., Galactic, the positions are recalculated from the positions entered originally, which is indicated by a small red asterisk next to the coordinates.

    Each row in the table represents one source with a name and some descriptive information. A row starts with a tick-box and an edit icon (Edit Source). The tick-boxes can be used to select one or more entries in the catalog for copy/paste as described in a later section. A shortcut to select all, or to deselect all catalog entries on the current page can be found above the table. Selecting and copy/paste (see below) has to be redone for every page. The Edit Source edit icon is used to access the details of the source entry in the catalog, i.e., the specifics of the source of interest. Here it will be a VLA calibrator source; later this might be the specifics of your scientific target source, and the information contained may be slightly different from entries in a personal source catalog created by an observer or by the automatic PST to OPT pre-filler.

    Select a random source (not J1118-4634) and expose the source details (click on the editing icon Edit Source in front of the name of the source of which you want to view the properties). The source properties in the main editing window are divided over three tabs, shown on top, labeled with the source's name, Images, and Notes. Most of the useful information is in the first tab, labeled with the source's name: the source name, its position, its velocity (if applicable) and its brightness (if applicable). The Images tab holds the Elevation curve for this source and the LST times for different elevation limits, which is useful for calculating LST ranges for which this source can be observed above a certain elevation. The Azimuth curve is also shown. Another useful piece of information is in the Notes tab. Press the blue circle with the white triangle/arrow (Expand Arrow) to show the VLA calibrator manual entry for this source (and press it again to hide this information). This and some extra information in a different form is given in the same tab under User Defined Values.

    Navigate back to the VLA catalog either by clicking VLA in the catalog column tree, or by clicking Return to VLA (or, e.g., DEC +10, depending on how you got there) at the top of the page. Please allow the web application to finish its operation and do not use the browser Back button.

    Other read-only catalogs may contain or use slightly different source properties and auxiliary information. In particular, the source names are those of the original catalogs; not necessarily according to the J2000 IAU convention as for the VLA catalog.

     

    Searching for Sources

    Select the VLA source catalog in the catalog tree at the left hand side and view the main editing window to the right. Source names follow J2000 IAU naming convention (i.e., truncated 10-character Jhhmm+ddmm) and aliases can be found by hovering over aliases or by viewing the source properties (through the editing icon \includegraphics[height=3mm]{psimg/source.png.ps}). To find source 3C279 may take a while, even if you know this source is J1256-0547 (note the capital "J") in the IAU convention. Entering 3C279 (note the capital "C") in the source search tool in the upper part of the left hand side column will search the selected source catalog for the source name in that catalog. If the "Search Aliases As Well" tick-box is not ticked, the search will only be matching for the name entered in the catalog (for VLA these are IAU names, but in your personal catalog you could have named your source 3C279 or "Skippy", etc); it then will only find this source in the VLA source catalog if J1256-0547 is entered. Therefore the aliases tick-box is by default ticked, but because searching is done on partial strings you may want to remove the option if you otherwise expect many matches (e.g., if you are looking for your source matching on the string "C" and don't want all 3C-sources to appear).

    Because the search is performed on a partial string, searching for "-" (a minus sign) in the VLA catalog, for example, will return a 16 page table with all VLA calibrators with negative Declination (J2000), plus some extra sources with a minus sign in the name if you left the "Search Aliases" checked. A search on 1331+ will return 3C286 (as J1331+3030). Searches should not be case sensitive, but sometimes weird returns happen if lower cases are supplied; use upper case (J, B, C) for the standard VLA calibrators and their aliases. Two wild-cards are allowed: "?" and "*"; they have the usual meaning of a single arbitrary character and any number of arbitrary characters, respectively. However, they are only useful between two other characters in the search string, as the search on string is automatically performed as a search on *string* (an empty search string returns the whole catalog).

    A source may also be obtained using the External Search if it is unknown to any of the existing catalogs. This search will be performed on the names, including aliases, in the SIMBAD database, using the same search and character rules.

     

    Advanced Search

    The Advanced Search (Figure 2.2) is used to search in an existing, selected catalog for other criteria than source name or alias. A common example is to search for a nearby calibrator at a position of your source of interest. This Advanced Search will bring up a dialog box in the main editing window containing various search parameter options. In that window, select the catalog(s) in which the search should be performed, and select the table(s) with the required parameters by checking the upper left tick-box of the relevant tables. Above the search parameter tables, you can select "All" or "None" catalogs and subsequently toggle individual catalogs. Table options and editing fields become active only when you select to use it. More than one catalog and more than one parameter table may be selected; the search interprets additional parameters as an AND condition. To perform the search, click the "Search" button below the parameter fields. Be patient, as searching can take a while; please do not continue clicking with the mouse button until the search operation has finished.

    Figure 2.2: Web browser screen shot of the Advanced Search options with an example of a cone search in combination with a minimum flux density. After you have selected your parameters, click the "Search" button for results.

    •  A Cone Search searches a radius, entered in degrees, around a position (J2000) or around the position of a source selected from any of the source catalogs by using the Select Source button (which brings up a dialog box to select a source from one of your catalogs). The resulting table should be sorted in increasing distance from the position; the table can be resorted if desired (by clicking table headers that turn orange). Positions are interpreted as decimal degrees if not supplied as, e.g., 1h 37m [41.3s] for R.A. and [+]33d 9' [35"] for Dec.; not supplied as a group of three numbers separated by a space or a colon, or otherwise not recognized as a sexagesimal entry. To activate the interpretation in the fields entered, click with the mouse button somewhere outside the boxes to validate the input. Always check the coordinates after entering each position or after pressing the Search button; it will replace your values with the interpretation of the validation procedure. You should check these values; the validation procedure will always be able to convert your entered values with these rules, but you are the only one to know whether the validation conversion is sensible!
    • Activating the Calibrator Code search allows a search for sources with a closure phase structure code (P, S, W, X) equal or better than the code selected for a certain observing band and VLA array configuration. This Calibrator Code is not to be confused with the the AIPS calibrator code (A, B, C, T) indicating a positional accuracy. Consult the VLA calibrator manual for more information on the definition of these codes and positional accuracy.
    • A Flux Density search searches for flux densities above the given limit in the selected observing band. This is of course only useful when flux densities are included in the catalog(s) selected.
    • The Name search is the same search action with the same string rules as for the string entered in the top search tool in the left hand side column, with the difference that here more than one catalog can be searched, and that other constraints can be included.
    • The Right Ascension and Declination searches are performed on a J2000 coordinate range, with the equal to or larger than (>=), or equal to or smaller than (<=) operators on the given limits. It uses the same rules on entering positions as for the Cone Search. When both limits are given, the search returns the sources between the limits (i.e., you will see proper results for a search on sources with R.A. between 23 and 01 hours).

    Figure 2.3: Web browser screen shot of results of the Advanced Search. Hovering with the mouse over details or aliases displays the source information (if available).

     

    Search Results

    Note that the sources matching the search parameters are listed below the Search Results header at the bottom. The results of a search are displayed read-only in the familiar SCT table format in a Search Results tree structure with the possibility to sort on different columns (Figure 2.3). Previous searches may be saved in the left hand column tree for convenience -- navigating to a previous search is done by simply selecting that search.  Sources presented in the Search Results can be selected, and added to a personal source catalog using copy/paste, etc. Search results are cleared when you log out from the SCT or the OPT web application.

    2.2. Creating a Personal Source Catalog

    Personal (re)source catalogs can be created, modified, and removed using the menu strip and icon menu at the top of the tools page. It is convenient to collect (re)sources for a specific project in a separate catalog, especially for convenience during schedule block creation and also, e.g., when sharing with co-I's.

    Usually NRAO has already been able to retrieve your sources from what you specified in your proposal. If this is the case you will find these in a source catalog, labeled with the project name in the left hand side column. You should follow the exercise above and examples below to get a feel for what is in your source catalog. You will want to check the entries in your source catalog, especially the accuracy of positions of your target sources, and the examples will help you check and/or modify the content.

    Copy/Paste from Existing Catalogs

    Regardless of how you create (or how NRAO fills) your source catalog entries, make sure they are correct before you continue with using them in the OPT. The OPT does not use global source properties; when you have modified a source you must use the OPT to reassign the new source separately to every scan that needs it. For this a Bulk Scan Edit has been implemented in the OPT (described later). Check your catalogs before making scans!

    Options from the icon menu and menu strip

    The icon menu is the line of little icons at the top of the (re)source catalogs in the left hand side column. They have the same functionality as the options from the menu strip (below), although not every menu strip option is represented as they are not used as often. Only basic cut/copy/paste and reordering can be done with this icon menu. Note that the actions selected from the icon menu apply only to editing in the left hand side column. Only valid actions will have an active icon in the menu, i.e., pasting an item may only be performed after copying or cutting the item first -- until then the paste-icon will appear grayed-out. Hovering over an item with your mouse will display a pop-up tool-tip help to remind you of the action attached to the icon, but we also show them for reference below:

    Cut Cut (or delete) selected tree item
    Page Copy Copy selected tree item
    Page Paste Paste selected tree item
    Arrow Up Move the selected catalog up in the tree
    Arrow Down Move the selected catalog down in the tree

    The same icon menu can be found in the RCT; for the OPT we will present additional icons for more options related to ordering scans in the OPT. Remember that these icons act only on the left hand side column items.

    The menu strip in the dark blue banner at the top of the page is used for creating new catalogs: FILE - CREATE NEW - CATALOG. It is not advisable to copy the VLA catalog personal catalog in a new personal catalog and add new target sources, but it is useful to copy VLA sources into a new or existing personal catalog. The menu strip options under FILE and EDIT are grayed out with a line through them if that particular option is not valid for the current selection (highlighted item in the catalog tree in the left hand side column). If the action you want to perform shows up as an invalid option (e.g., EDIT - CUT - GROUP to delete your group of sources) this usually means that you are not at the right place in the tree (e.g., not in the group, but in the upper level catalog). The names of the actions are quite self-explanatory, so we only list them for reference in the table; the ones in square brackets only appear when relevant, in particular when a source in a group is selected. A similar list of menu strip options is available in the RCT and OPT, but with options specific to the tools. The menu strip options may act on both items in the left hand side column as well as items in the main editing window.

    FILE CREATE NEW CATALOG EDIT [ADD TO GROUP] -  -> [[group name]] HELP ABOUT THE SCT
    GROUP [REMOVE FROM CURRENT GROUP] ABOUT ME
    SOURCE CUT CATALOG DOCUMENTATION
    EXPORT XML... GROUP CONTACT SUPPORT
    EXPORT PST... SOURCES
    IMPORT COPY CATALOG
    EXIT GROUP
    SOURCES
    PASTE CATALOGS
    GROUPS
    SOURCES

     

    Adding Sources to Your Personal Catalog

    There are three ways to add sources to a personal catalog, each described below. A fourth one is that the OPT gets filled with information from the PST once the TAC has approved observing time for your project. If you find a catalog imported directly from the PST, please carefully check the target source positions before you start using them in the OPT as you may have not entered them in the PST as you want them to appear in the SCT/OPT.

    Importing Source Lists, Including Sources Entered in the PST

    If you or a co-investigator uploaded a source list with your proposal in the PST, and this source list has not been transferred from the PST (or you prefer to delete that one), you should be able to get a head-start by uploading the same source list to the OPT. Use FILE - IMPORT... to communicate with a dialog box. Choose PST as input format and name your source catalog after it has been uploaded by selecting the New Catalog and navigating to the Properties tab. As a reminder, the PST format is/can be found in the relevant section of the PST manual (or in the complete description) in case you decide to make such a file at this stage. You may want to check the details of some sources to verify that the information has ended up correctly in the source property definitions. Verifying it now may save you more trouble later on when creating SBs.

    Copying Sources from Existing Catalogs

    It is likely that your anticipated calibrator sources (which may not have been included in the proposal cover sheets) are already defined in, e.g., the VLA calibrator source catalog. You can search for calibrator sources using the search tool described earlier in this chapter. In the catalog (or group) or in the search results you can select one or more sources you desire to add to your personal catalog by ticking the check-box(es) in front of the source name and editing icon using the top menu strip EDIT - COPY - SOURCES, etc. Then select the destination catalog or group and simply paste the copied sources: EDIT - PASTE - SOURCES, etc. You must repeat this action for each catalog or search results table page. Again verify that the source information in your personal source catalog is correct, e.g., by adding additional digits to a source position, prior to assigning source information to scans in the OPT. An example sequence would be as follows:

    • Make sure you have navigated to the SCT.
    • From the top menu strip, select FILE - CREATE NEW -  CATALOG; you can skip this step (and the next step) if the catalog you want to use already exists and is writable (i.e., the catalog name is not in slanted red font), e.g., the catalog automatically
      generated with your project ID.
    • Your new catalog with the default name [New Catalog] appears in the main editing window, in the Properties tab. Change the name of the catalog to something useful to remind you of its purpose.
    • Optionally add the names of coauthors that you want to share the catalog with and who may edit the sources in the catalog.
    • At this stage you can opt to group your sources. This is not necessary, but convenient if you are going to have many sources. If you want to group sources in this catalog, select FILE - CREATE NEW - GROUP, and name your group under the Properties tab.
    • Click to navigate back to the first tab: Sources.
    • Select the VLA source catalog and perform your source search as described previously; use Advanced Search or External Search if necessary.
    • In the source table to the right, in main editing window, check the source(s) you want. If you don't know which source to select, study the details of each before selecting one. If there are more sources than fit on a page you can change the number of sources per page from 25 to 50 or 100, or use multiple actions to select all your sources in subsequent steps.
    • From the top menu strip, select EDIT - COPY - SOURCES.
    • Select your newly named source catalog (or group within it).
    • From the top menu strip, select EDIT - PASTE - SOURCES. If there are groups in the catalog, you will have the option to add them to a group as well. The sources now show up on the right hand side.
    • This can also be achieved by copy/paste of entire groups and/or entire catalogs using the top menu strip options or the menu icons at the top of the (left hand side) source catalog column. Use the fly-over tool-tip help to identify the proper icon for each action.
    • Maybe you want to check the source properties using the Show/Edit icon for each catalog entry. You can also reorganize your sources by adding groups (FILE - CREATE NEW - GROUP) and move your sources around using the column icon menu, or using EDIT in the top menu strip. Unwanted sources can be deleted using Cut.
    • If you are unhappy with the name of the catalog or group you can always rename it by highlighting it and then clicking on the
      Properties tab.

    Note that sources do not have to belong to a group. If you have specified groups, sources that do not belong to that group will not show up if you select that group. When there are sources in groups and sources not belonging to a group in the same catalog, you can only see and select a source without a group when you select the entire catalog.

    Entering Source Information from Scratch

    If you do not use the PST upload file and your source does not appear in any of the existing catalogs, you would create a new source in a source catalog (or group) after selecting (or creating) the catalog or group you want to place the source in: (FILE - CREATE NEW - CATALOG/GROUP,) FILE - CREATE NEW - SOURCE. You will be presented with a blank source page consisting of three tabs (or pages) labeled New Source, Images, and Notes. Name your source something convenient to search for at a later point, and fill in the necessary details (see below). You may also care to fill in the origin of your data for your own reference (e.g., PST file name, SIMBAD data base, scooped draft paper, etc.).

     

    Source Positions

    There are four different types of positions you can enter: a Simple Position, a Position with Polynomial Terms, Solar System Body with Internal Ephemeris, and Solar System Body with Uploaded Ephemeris. By default the first tab-page uses Simple Position below the source name and aliases. Select a coordinate system (Equatorial, Galactic or Ecliptic) and equinox in which you specify the coordinates and, if you care, also supply a distance (if known). For anything else than the Simple Position use the drop-down menu. The new selection will redraw the position table accordingly with all variables defaulted. You can select a predefined Solar System body name, upload an ephemeris table, or you can specify the position and some motion terms valid for some time range. Motion terms are entered as polynomials in time [display]\rm position\ at\ Reference\ Time\ in\ Equinox + value(1) \times time + value(2) \times time^2 + value(3) \times time^3,  etc [/display] Press the [+] for each extra motion term, enter the value and choose the order of the polynomial in time. The motion term units and uncertainty will help recalculating the position (and error) at the time of observations, though this is currently not yet fully tested. Leave the motion terms at zero if the source is considered not to move in the specified time interval. If you need another position and/or different motion terms for another time interval, simply add another position to the previous one. Delete old or obsolete positions using the tick-box in the upper left of a position table and REMOVE SELECTED POSITIONS. More information is given in the Observing Guide under Moving Objects.

     

    Adding Information

    In addition to specifying a position, some extra reference information may be specified for this catalog entry. These items however are not necessary for the observation and are provided for your own reference.

    Source Velocities

    In the next table, under Source Positions, Source Velocities can be entered using the Add button (Figure 2.4). Enter the value and select a rest frame and rest frame convention. Just like a position you can add more than one velocity, but valid for another frequency range. Removing old or obsolete velocities is also a very similar procedure: tick the unwanted velocity and use REMOVE SELECTED.

    Note however, that source velocity information is not used anywhere in the OPT or in the observations, nor is it transferred with the data. Source velocity information entered here is purely a user supplied comment, just like brightness and image links below or distance above. The proper place to enter a source velocity is in the resource of the scan, where Doppler corrections are calculated for the time of observing. How to do this is explained in the "Creating your Resource" section.

    Figure 2.4: Adding a source velocity.

    Source Brightness

    Similar to specifying a source velocity, with ADD you can specify a source flux density and distribution. You are asked which type of brightness distribution you want to add to your source properties. For unresolved (point-like) sources you would probably choose type Point, and fill out the Flux Density at some Frequency Range. A slightly resolved source perhaps would be better described by a Gaussian model with a Major Axis and Minor Axis Diameter at some Position Angle. Planets also use the Limb Darkening property of the Disk models. You can specify more than one brightness model for a source, or provide a FITS image or clean-components model file. The actual parameters differ for each flux distribution model. A source brightness model is simply removed with ticking a check box and REMOVE SELECTED.

    Images tab

    This tab displays the Visibility Chart consisting of the elevation and azimuth of the source as function of LST together with a table of rise and set LST (at 8° elevation) and some other elevation/azimuth and LST properties for your reference. Below are Image Links. It allows you to keep a catalog of image URL links, e.g., to the images in the VLA archive; use ADD or REMOVE SELECTED as many times as desired.

    Notes tab

    This tab-page is where you can collect all other information you wish to attach to this source. For example, for a target source you can remind yourself of the nearby calibrators you have found to be useful at some frequency, a reference to a paper mentioning an alternate position or a source property, or anything else you want to note. Click the blue expand button or New Note to add information to the Notes field. You can add links to papers or any other URLs for that matter. User defined values can be added at the bottom, e.g., the UV-range you determined to be proper for a point source calibration model, or whatever you deem useful.

     

    Final check

    After all this data entering, make sure you check your catalogs for correctness. It is important that your source positions are correct before creating scans in the OPT and before storing to disk or sharing your catalogs with your collaborators.

    2.3. Setting Up Pointing Scans and Tipping Scans

    Pointing scans are typically done at X band (8 GHz) on strong (> 0.3 Jy/beam) continuum sources near your target source, i.e., within about 20 degrees. Most likely you will find such a source in the VLA calibrator catalog. Note that for longer tracks, the optimum pointing source is at roughly the same Declination and about 10 degrees earlier in LST (40/cos(Dec) minutes in RA), but the source itself (if bright enough in X band) is also a relatively safe bet. You may want to add the pointing source to your personal source catalog if it is not in there already. If you plan on doing secondary reference pointing scans (see the next chapter) and your intended pointing source is not strong enough at the observing frequency you wish to use for the secondary reference pointing scan, you may need to add another pointing source that is strong enough at this frequency, or perhaps even revisit your first choice. More details can be found in the Observing Guide.

    Tipping scans currently are not supported, but will be in the near future. This text will be updated at that time.
    Tipping scans on the other hand are typically done independently of your sources. The only interest is the observing frequency and the direction, in Azimuth, of the main distribution of your sources. Tipping scans currently are set up in the OPT only; no extra sources are needed. However, tipping scans are not allowed at this time.

    3. Frequency Band Nomenclature and Using the Resource Catalog Tool (RCT)

    3.1. Orientation and Nomenclature of Frequency Chunks in the OPT

    Assuming you already have successfully logged in to the OPT web application, and assuming that there is no message in the Important message banner that makes you decide to abandon the OPT for the moment, look for the navigation bar at the top. If Instrument Configurations is not in bold face, but in normal font and underlined, click it with your mouse button to navigate to the RCT (Figure 3.1). To exit the tool properly use the Exit link in the upper right corner or with FILE - EXIT; do not kill the browser window/tab.

    A short introduction to the layout of this tool's page has been given in the introduction (Chapter 1). There should be at least one NRAO Defaults catalog visible in the left hand side column, the catalog browser. Like for the SCT, for orientation and to get a feel for the tool(s), it is instructive to walk through this catalog. After this orientation it should be almost intuitive to create your own personal resource catalog(s) which you will use in your project's SB scans or help to understand how to use one of the standard wide band resources provided in the NRAO Defaults catalog. Note that a resource catalog for each of your successful proposals may be pre-filled (if you are the PI or contact for the proposal); it is important that you check the pre-filled information for correctness.

    Figure 3.1: Web browser screen shot of the RCT opening page.

     

    Example of a Resource Catalog: NRAO Defaults Catalog

    Be aware that data from the WIDAR correlator is different from the old VLA correlator in the sense that data is always delivered in spectral line or pseudo-continuum mode, similar to Very Long Baseline Interferometry (VLBI) practice. When referring to continuum below, it is meant to refer to data taken for wide band observation purposes: the data itself is divided in frequency channels, but the scientific interest is in the data averaged over all channels and not in individual channels with line emission (or absorption). The latter is referred to as spectral line data. This is the difference in obtaining a two-dimensional image of the sky versus a three-dimensional image cube, where the data retains that different frequencies show different (two-dimensional) sky images.

    The best continuum sensitivity is obtained using the maximum available bandwidth in the most sensitive part of the observing band, and thereby avoiding Radio Frequency Interference (RFI) as much as possible. The resource which gives the best performance in each observing band is defined in the NRAO Defaults catalog. To describe the setups, is it useful to understand how the basic generalized path of the radio frequency (RF) signals collected by the receivers in the antenna are delivered through the intermediate frequency (IF) electronics to the WIDAR correlator and where the correlated data ends up in a data set.

    baseband

    Figure 3.2: Simplified schematic of nomenclature and the involvement of the 8-bit and/or 3-bit sampler choice in yielding one 1 GHz or two 2 GHz basebands for each of the two independent IF paths (AC and BD) from the (up to) 5 GHz down-converted RF bandwidth delivered by the receivers. Per IF path an 8-bit or a 3-bit sampler can be chosen independently; a baseband pair consists of RCP and LCP signals (or linear polarization X and Y) at the same frequency. After being defined at the antennas, these baseband pairs (A0C0) or (A1C1 and A2C2) as well as (B0D0) or (B1D1 and B2D2) are then transported over optical fiber to the WIDAR correlator in the control building for processing.

     

    Baseband Pairs

    The receiver in the antenna passes (up to) 5 GHz down-converted frequency of the RF receiver bandwidth to four signal paths (Figure 3.2); two right circular polarization signals (RCP), labeled IF A and IF B, and two left circular polarization signals (LCP), labeled IF C and IF D. IF A and IF C (i.e., one RCP and one LCP) signals are tuned to the same RF frequency and thus may produce a Stokes I signal from the source. IF B and IF D are also tuned to the same frequency, which typically is not the same tuning as for IF A and IF C. These IF signals are then sampled independently using 8-bit samplers or 3-bit samplers. The Observational Status Summary Sampler page should aid in which sampler to use for your observations. The 8-bit samplers each yield a one 1 GHz wide frequency range containing a corresponding 1 GHz down-converted RF range. The 3-bit samplers each yield two 2 GHz wide frequency ranges containing two corresponding 2 GHz down-converted RF ranges. Per IF path (AC or BD) the two 2 GHz ranges from the 3-bit samplers must be within a total range of 5 GHz and are typically placed to yield a continuous 4 GHz RF bandwidth per IF path, or an 8 GHz RF bandwidth total.

    The individual sampled frequency ranges are referred to as basebands, in particular baseband pairs when a combination of simultaneously tuned RCP and LCP signals is involved. The 8-bit samplers yield 1 GHz baseband pairs which are labeled A0C0 or B0D0, depending on the original IF path. The 3-bit samplers produce 2 GHz baseband pairs labeled A1C1 and A2C2 as sampled from IF path AC, or B1D1 and B1D1 if the signals are sampled from IF path BD. These baseband pairs are then transported over optical fiber from the antennas to the correlator.

    Part of setting up the resource is to specify which samplers are used and to specify the baseband pair center sky frequencies.

    Subband Pairs

    When the basebands from each antenna reach the correlator room, they are fed in 128 MHz bandwidth intervals into station boards. This regular pattern of 128 MHz creates a fundamental interval boundary which cannot be observed, nor included in processing of nearby frequencies. Apart from the baseband edges, there are 7 of such unobservable frequency boundaries per 1 GHz (1024 MHZ) baseband when using the 8-bit sampler, and 15 per 3-bit sampler baseband (i.e., per 2 GHz, per 2048 MHz). Note therefore that, since this is an odd number, the chosen baseband center sky frequency never can be observed: do not place the baseband center at the frequency of your spectral line! From each 128 MHz chunk, the station boards determine which part (central frequency and frequency width) is forwarded to the correlator for processing. That is, per polarization for each 128 MHz bandwidth it is determined whether the signal should be forwarded to the correlator, and whether each 128 MHz bandwidth should be divided in powers of 2 and tuned to another center frequency within the 128 MHz range, provided that the frequency interval does not cross the boundary when forwarded to the correlator.

    The filtered and tuned frequency ranges delivered by the station boards are referred to as subbands, in particular subband pairs for simultaneously tuned RCP and LCP signals. The individual subbands are at most 128 MHz wide, and independently tunable in frequency if reduced in width by powers of two without crossing the 128 MHz boundaries. Per resource, up to 64 subband pairs can be defined.

    Part of setting up the resource is to specify the frequency tuning and frequency width of the subbands that are to be used.

    correlator

    Figure 3.3: Simplified schematic of nomenclature of correlator components. Up to 64 baseline board pairs process the baseband pair streams from the antennas as formatted by the station boards in four quadrants (Q1-Q4). A resource in the RCT defines the output of the station boards (after defining the baseband pairs at the antennas) and the assignment of the available baseline board pairs for processing to yield up to 64 independently configurable subbands with spectra. These subbands will end up as a simultaneously observed subset of spectral windows (SpWs) in the visibility data. At most one subband (of 128 MHz or less bandwidth) can be processed per baseline board pair, but more than one baseline board pair can be used to process the same subband (called baseline board stacking), yielding a larger number of channels to obtain an increased spectral resolution over the bandwidth of that subband (in the case without recirculation).

     

    Baseline Board Pairs

    The resulting subband pairs per antenna and IF path are presented to one of the four correlator quadrants for processing by pieces of hardware known as baseline boards, or baseline board pairs when the subband contains both RCP and LCP signals (Figure 3.3). There are 16 baseline board pairs per correlator quadrant.  A single baseline board pair can only receive data from a single subband for processing. Per baseline board pair 256 correlation products can be computed, where the number of products is the number of polarization products (1, 2 or 4) times the number of spectral frequency points (256, 128 or 64). Within the limits of the number of baseline boards in a correlator quadrant, more than one baseline board can be assigned to process a single subband pair (thus up to 16) at the cost of processing other subband pairs. Assigning more than one baseline board to a single subband is referred to as baseline board stacking. Without recirculation, the combination of subband width, number of polarization products and number of baseline boards determine the channel frequency width of the data in the subband. The Observational Status Summary contains more details about the WIDAR correlator.

    Part of setting up the resource is to specify the distribution of the computing power of the baseline board pairs over the active subbands.

    Spectral Windows and SDM/BDF Data Archive

    The correlated data consists of up to 64 independently tunable (center frequency and frequency width) and configurable (polarization and spectral frequency points) subbands per observing resource. This data is written as Binary Data Format (BDF) files to the archive, together with header and auxiliary information defining the corresponding Science Data Model (SDM) for the observation. Multiple resources can be used during an observation, and therefore many more than 64 subbands can be in the data; subbands contained in the SDM/BDF are called individual spectral windows (SpW) in CASA (or IFs in AIPS). CASA can process non-homogeneously configured spectral windows simultaneously, but care must be taken in the interpretation of spectral windows versus subbands when referring to an observing resource: any resource can have up to 16 or 64 subbands (for 8-bit and 3-bit respectively) but a data set may contain hundreds of spectral windows (from multiple resources).

    OPT figure 2.2

    Figure 3.4: Web browser screen shot of the RCT when NRAO defaults is selected.

    NRAO Defaults

    The NRAO Defaults catalog (Figure 3.4) is a collection of hardware and instrument configurations (front-end receivers, correlator integration time plus observing/subband bandwidth and frequency channels, frequency tuning, etc.). They are expected to be good standards for wide band continuum observations using the VLA.

    The NRAO Defaults catalog is in red italics and has a plus-icon in front of it. Remember that this means that this catalog is read-only and has groups. Very much like was explained for the SCT tool in a previous section, if you click the plus-icon (xpnd) or "NRAO Defaults" these groups will appear in the catalog tree.  Similarly, clicking "NRAO Defaults" differs from clicking the plus-icon in that it will expose the total content of the catalog in the main window, with 25 sources per page, starting with a pointing resource group. As there are more default resources than 25 for the A/Any config group, the top and bottom of that table displays a small page navigation menu.

    Pre-defined resource groups in the NRAO Defaults catalog are Pointing setups and a number of array configuration dependent groups.  During the commissioning of the correlator, different commissioned resources were tied to the array configuration dependent groups. When a group is highlighted or selected using the mouse button, the right-hand side window with the contents will only show (filter) the resources which were grouped in this sub-catalog. For example, selecting the A/Any config group will now only list the NRAO default resources for wide band observations in the A array configuration (any band). Similarly, the Pointing setups will show the NRAO default resources for pointing scans in C and X band (see below).

    Each line in the table represents one resource with a name and some descriptive information. A line starts with a tick-box and an edit icon (Edit Source). The tick-boxes can be used to select one or more entries in the catalog for copy/paste as described in the SCT catalog chapter. Selecting and copy/paste has to be redone for every page. The Edit Source edit icon is used to access the details of the resource entry in the catalog, i.e., the specifics of the resource of interest. Here it will be a NRAO default resource, but later this might as well be the specifics of your scientific target resource, and the information contained in these entries therefore may be slightly different from entries in a personal source catalog created by an observer or the automatic PST to OPT pre-filler.

    Click NRAO Defaults in the left-hand side column to return to the NRAO Defaults catalog.  The basic catalog rules, use of icons, browsing, table viewing, and the mechanics of creating and editing of source catalogs is almost identical to that of the SCT tool. So to access the details of a single resource, click the edit icon (Edit Source).

    Default Wide Band Continuum Resources

    Continuum observations are generally performed using the maximum available bandwidth to obtain the best signal to noise ratio for a signal that is (mostly) independent on frequency. The receivers for the upper three receiver bands (> 18 GHz: K, Ka, Q) cover more than 8 GHz bandwidth. To obtain maximum instantaneous sensitivity it is therefore possible, with the 3-bit samplers, to observe a full 8-GHz wide bandwidth for continuum purposes. On the other hand, signals obtained with the lower frequency receivers, where RFI is apparent and the receiver coverage is less than 4 GHz, are better sampled with the 8-bit samplers covering up to 2 GHz bandwidth. For C, X and Ku bands, one has to choose. Below, examples of a 3-bit and an 8-bit sampler default wide band resource are shown.

    High Frequency 8 GHz Wide Band Continuum (3-bit, K, Ka and Q band)

    As an example of a 3-bit wide band continuum resource, select the K64f3 wide resource in the NRAO Defaults catalog (in group DCB/Any config).  Click on the (Edit Source) edit icon (with fly-over help tool-tip Show/Edit properties for this catalog entry) to see the hardware and instrument options used in this resource.

    Figure 3.5: Web browser screen shot of the RCT when the default setup for K band is selected.

    The information displayed (Figure 3.5) in the top graphic is the receiver band coverage, one color per IF path, four in total. Furthermore the nominal (green, 1dB sensitivity drop) and extreme (white, 3dB) receiver coverage ranges are shown as vertical dashed lines. A small table shows a summary of correlator resources used for this setup, which will update when further specification is made. Note that this non-editable default resource uses the maximum of 64 baseline board pairs to cover 8 GHz of bandwidth within the allowed data rate. Below the graphic is a window with six tabs: Basics, Lines, Basebands, Line Placement, Subbands and Validation. For simple wide band observations ignore the Lines and Line Placement tabs.

    The Basics tab displays the name (K64f3 wide), receiver band (K) and the correlator integration time (3.0s to remain within the allowed data rate).

    The Basebands tab summarizes the samplers in use and the central sky frequency to which each of the four (2 AC + 2 BD) 2-GHz wide baseband pairs are tuned, with their individual sky range bandwidths.

    The Subbands tab lists, for each baseband under a different tab, the subbands as configured for the baseband. In this case there are 16 subbands of 128 MHz per baseband, each distributed over a single correlator quadrant (displayed by different colors, see also at the bottom of the Validation tab). Each subband will yield 64 spectral frequency points at full polarization. This setup thus will generate 64 spectral windows in the data; each 128 MHz wide divided in 64 2-MHz wide channels and 4 polarization products.

    The Validation tab summarizes the setup in receiver band and correlator integration time, baseband properties in the next table, and subband properties. Note that because the "yellow" baseband is centered at 19.000 GHz, and the baseband is not 2.0 GHz wide, but slightly wider at 2048 MHz, some (24 MHz) of the baseband is actually below the official 1dB limit of 18.0 GHz. This generates a warning, but in practice is not as serious as it appears.

    Navigate back to the NRAO Defaults catalog either by clicking NRAO Defaults in the catalog column tree, or by clicking Return to NRAO Defaults (or DCB/Any config, depending on how you got there) at the top of the page. Please allow the web application to finish its operation and do not use the browser back button.

    Low Frequency 1 and 2 GHz Wide Band Continuum (8-bit, P, L, and S band)

    As an example of an 8-bit wide band continuum resource, open the S16f5DC resource in the NRAO Defaults catalog (in group DCB/Any config).

    Figure 3.6: Web browser screen shot of the RCT when the default setup for S band is selected.

    The information in the top graphic (Figure 3.6) now shows only two colors, one per IF path. This is a direct result from choosing the 8-bit sampler in the Basebands tab. The number of baseline board pairs used in this setup is only 16 to cover 2 GHz of bandwidth.  The Basebands tab lists two (1 AC + 1 BD) 1-GHz wide baseband pairs with their tuning centered in S band.  Through the Subbands tab, and the tab per baseband it is seen that there are 8 subbands of 128 MHz per baseband, each distributed only partly over the available correlator quadrants (per color used) to yield 64 full polarization spectral frequency points. This setup generates 16 spectral windows in the data, the number of colored items in the correlator quadrant summary under the Validation tab. Here also the subbands are 128 MHz wide divided in 2-MHz wide channels.

     

    Spectral Line Observations

    There is no separate example of a spectral line resource in the NRAO Defaults catalog. The WIDAR correlator writes all its data in spectral line format, meaning that the continuum resources described above are already spectral line resources with 2 MHz frequency channels. However, when the scientific interest is in a specific line, typically one would want to use a spectral resolution that is better than the 2 MHz channel width in the continuum resources above. The correlator would be set up to provide data with narrower frequency channels than 2 MHz, tuned to the line frequency when corrected for (approximate) Doppler shift. Note that the channel frequency width is not the final spectral resolution in the data cube as this depends on the actual data processing and whether, e.g., Hanning smoothing was applied in post processing. Smoothing will decrease the spectral resolution in the data. When planning on smoothing, be aware that the channel width only approximates the best spectral resolution available without smoothing, at about 1.2 times the individual channel separation. To get a particular spectral resolution with Hanning smoothing make sure that the line is oversampled with at least a factor of two (i.e. double the number of channels that you need for that spectral resolution). There are four possibilities to reduce the width of the frequency channels to obtain frequency channels narrower than 2 MHz for spectral line work; they can be used independently or simultaneously.

    • The number of polarization products may be reduced from 4 to 2 or 1 to obtain contiguous 128 MHz subbands with a spectral channel separation of 1 or 0.5 MHz respectively.
    • The subband bandwidth of 128 MHz can be reduced in factors of two to obtain factors of two narrower channel separations in that subband.
    • When the subband bandwidth is reduced, processing capacity becomes available to process more lags. This is known as recirculation. The product of bandwidth and recirculation factor should be less than 128 MHz per subband.
    • Processing of fewer subbands than the maximum of 64 allows the use of additional baseline board pairs to produce more channels. This is known as baseline board stacking.

    See the Observing Guide, Spectral Line section, and the Observational Status Summary, WIDAR section, for more information, but also read the below..

    3.2. Creating a Personal Resource Catalog

    3.2.1. Introduction and Wide Band Continuum Resources

    It is possible that NRAO has already been able to retrieve your resources from what you specified in your proposal.  If this is the case you will find these in a resource catalog labeled with the project name in the column at the left.  However, you should follow the examples below to get a feel for what is in your resource catalog. You will want to check the entries in your resource catalog, especially if you require specific frequency settings, and the examples will help you check and/or modify the content.

    When you are planning simple wide band observations at default VLA frequencies only, and thus all anticipated resources are already defined in the "NRAO Defaults" catalog, it is still strongly suggested that you make separate personal catalogs for your different PBs/SBs, e.g., in the catalog with the proposal ID generated automatically. Simply copy the resource of interest (including pointing resources if needed) from the "NRAO Defaults" catalog to your project catalog.  Not only will the reason become clear later on, it also creates an opportunity to get used to the tool and you will find that scheduling using small catalogs will be faster over the web interface.  If you plan a spectral line observation, it is instructive to read the wide band case first as this saves repeating information.  Resources for wide band and spectral line observations may be mixed in the same resource catalog and resource group.

    Wide-band resources

    The observer has the following choices, described in the next two sections:

      Please consult the Guide to Observing with the VLA about setup-scans and 3 bit resources.

      Using an NRAO default

      Suppose your SB consists of VLA default frequency full polarization wide band observations in C band and in Ka band, and that you want to populate your personal catalog in first instance with these default (polarization) wide band resources. For this particular example, this is what to do: Option 1 uses the Resource Wizard, Option 2 uses predefined NRAO resources..

      • Make sure you have navigated to the RCT, shown in the navigation strip as Instrument Configurations.
      • From the top menu strip, select FILE - CREATE NEW - CATALOG; you can skip this step (and the next step) if the catalog you want to use already exists and is writable (i.e., the catalog name is not in slanted red font), e.g., the catalog automatically generated with your project ID.
      • Your new catalog with the default name "[New Catalog]" appears in the main editing window. Change the name of the catalog to something useful (to remind you of its purpose) by navigating to the Properties tab.
      • Optionally add the names of coauthors that you want to share the catalog resources with and who may edit the resources in the catalog.
      • At this stage you can opt to group your resources. This is not necessary, but convenient if you are going to have many resources. If you want to group resources in this catalog, select FILE - CREATE NEW - GROUP, and name your group under the Properties tab.
      • Click to navigate back to the first tab: Resources.

      Option 1, using the Wizard:

      • Select from the top menu strip FILE - CREATE NEW - 8/3-BIT INSTRUMENT CONFIGURATION
      • For 3-bit configurations, a pop-up will request inputs for the band, array configuration and polarization products, for 8-bit configurations you are taken directly to the Basics tab to select the band and the correlator integration time.
      • Upon selecting, name the resource, (select band) and confirm the integration time (which is set to the default) in the Basics tab.
      • Optionally change the Baseband center frequencies in the third Basebands tab and validate in the Validation tab.

      Option 2, copying an NRAO template:

      • Select the NRAO defaults resource catalog and e.g., D/Any config group.
      • In the resource table to the right (main editing window), check C16f5 wide and the Ka band wide band option you want (i.e., Ka64f3 for 8 GHz full polarization, or perhaps Ka16f3 for 2 GHz bandwidth). If you don't know which Ka band resource to select, study the details of each before selecting one, or simply select all. If you selected a group first (and not the whole NRAO Defaults catalog), you may not be able to select both bands in one go; simply repeat these steps. If the resources are not on the same page when selecting the whole NRAO Defaults catalog, simply change the number of resources per page from 25 to 50 or 100.
      • From the top menu strip, select EDIT - COPY - INSTRUMENT CFGS..
      • Select your newly named resource catalog (or group within it).
      • From the top menu strip, select EDIT - PASTE - INSTRUMENT CFGS.. The resources now show up on the right hand side.
      • This can also be achieved by copy/paste of entire groups and/or entire catalogs using the top menu strip options or the menu icons at the top of the (left hand side) resource catalog column. Use the fly-over tool-tip help to identify the proper icon for each action.
      • Maybe you want to check the resource properties using the Show/Edit icon for each catalog entry, especially if you copied one of the Ka band resources as you would probably want to check the polarization or channel separation for each. You can also reorganize your resources by adding groups (FILE - CREATE NEW - GROUP) and move your resources around using the column icon menu, or using EDIT in the top menu strip. Unwanted resources can be deleted using EDIT - CUT - INSTRUMENT CFGS. and similarly unwanted groups or catalogs can be removed using EDIT - CUT - CATALOG/GROUP or by using the scissors in the icon menu.

      If you are unhappy with the name of the catalog or group you can always rename it by selecting it and then clicking on the Properties tab. If you want to change some parameters, choose the relevant items in the next list. Refer to Figure 3.4.

       

      Create your own resource from scratch

      • Make sure you have navigated to the RCT, shown in the navigation strip as Instrument Configurations.
      • From the top menu strip, select FILE - CREATE NEW - CATALOG or select an existing personal catalog.
      • Your new catalog with the default name "[New Catalog]" appears in the main editing window. Change the name of the catalog to something useful (to remind you of its purpose).
      • Optionally add the names of coauthorss that you want to share the catalog resources with and who may edit the resources in the catalog.
      • At this stage you can opt to also group your resources. This is not necessary, but convenient if you are going to have many resources. If you want to group your resources in this catalog, select FILE - CREATE NEW - GROUP,  and name your group under the Properties tab.
      • Click to navigate back to the first tab: Resources.
      • From the top menu strip, select FILE - CREATE NEW - 8/3-BIT INSTRUMENT CONFIGURATION. You will be presented with, e.g, the 3-bit resource page for which an example is shown in Figure 3.7:

      Figure 3.7 - 3-bit resource page. Note how the four 2GHz basebands cover 8GHz in K-band

      • In the first (Basics) tab, name your resource, select an observing band and enter some descriptive information in the comments field at the bottom of the page (not shown here).
      • Choose a correlator visibility integration time, in integer seconds with a minimum of 1 second, or use 5 seconds if you don't really care; the latter will reduce the size of the data set at the cost of time-averaging smearing away from the phase center. The correlator integration time may have to be adjusted later to remain within the maximum data rate for the specific setup you are creating.
      • Move to the Basebands tab (i.e., skip the Lines tab).
      • For the high frequency bands (K, Ka, and Q) the default is to use 3-bit samplers covering 8 GHz bandwidth using four 2 GHz basebands, but you may select the 8-bit system to use two 1 GHz basebands. For the low frequency bands the default is to use the 8-bit setup.
      • For each baseband select the baseband center frequency if the defaults won't work for you. If you plan on doing this remember the restrictions: for 3-bit the baseband centers for A1C1 and A2C2 must be within about 2.5 GHz (same for B1D1 and B2D2), and in cases where AC and BD are spread over a large range usually AC needs to have the upper center frequencies. Ka band has extra restrictions (see below or the OSS). Ignore the Doppler table below the baseband center frequency table.
      • Continue to the Subbands tab (i.e., skip the Line Placement tab).
      • Under every baseband tab (i.e. repeat this four or two times) click Fill Subbands. Each defined subband will fade a fraction of the color of the baseband in the graph on top.
      • If you are unhappy with any of the subbands you can delete individual subbands with the delete icon (delete) at the right hand side of the subband table. Mulitiple subbands can be selected and deleted with the Delete Selected Subbands button.
      • Subbands can be changed individually, or be selected and bulk-edited using Bulk Edit Selected Subbands. Note that editing is limited to the current baseband tab only; if you, e.g., want to change the polarization of the whole observation you have to repeat the editing in each of the baseband tabs. You can only enter the center frequency for subbands of 16 MHz and narrower, provided that they do not cross a 128 MHz boundary; wider subbands can only be selected from a fixed drop-down list.
      • You may sacrifice subbands in favor of more correlator products (channels or polarizations) in another subband. More of this will be described in the Spectral Line Resources section below.
      • If you want to start anew (using the already specified baseband centers), click Clear All Subbands to remove all subbands in all basebands, or delete the resource (or Group, Catalog) completely using the menu strip or icon menu.
      • Finally use the Validate tab to inspect your setup in terms of frequencies and correlator resources (i.e., baseline board pair allocations). Check your resource, from top to bottom. If you create more than one resource, check each of the resource properties using the Show/Edit icon for each catalog entry. You can also reorganize your resources by adding groups (FILE - CREATE NEW - GROUP) and by moving your resources around using the column icon menu, or using EDIT in the top menu strip. Unwanted resources can be deleted using Cut.
      • If you are unhappy with the name of the catalog or group you can always rename it by highlighting it and then clicking on the Properties tab.

      Incorrect or unfinished template resources — the ones which generate red errors in the interface feedback strip — will be saved for future use, when you exit and log in again. They will however not be usable when assigned to a scan in the OPT. The resource first must be fixed in the RCT after which it can be assigned to a scan in the OPT. Resources with warnings can be assigned to a scan, but the warning should be understood before continuing with OPT scheduling. This behavior also applies to sources in the SCT.

      Regardless of how you create (or how NRAO fills) your resource catalog entries, make sure they are correct before you continue with using them in the OPT. The OPT does not use global resource properties; when you have modified a resource you have to use the OPT to reassign the new resource separately to every scan that needs it.  For this a global edit has been implemented in the OPT. Check your catalogs before making scans!

      Options from the menu strip and icon menu

      In the previous recipes some usage of the options in the menu strip were given (e.g., FILE - CREATE NEW - CATALOG). The names of the actions are quite self-explanatory, similar to the menu strip options in the SCT:

      FILE CREATE NEW CATALOG EDIT [ADD TO GROUP]   -> [[group name]] HELP ABOUT THE RCT
      GROUP [REMOVE FROM CURRENT GROUP] ABOUT ME
      8-BIT INSTRUMENT CONFIGURATION CUT CATALOG NEW FEATURES
      3-BIT INSTRUMENT CONFIGURATION GROUP DOCUMENTATION
      EXPORT ...
      INSTRUMENT CFGS. CONTACT SUPPORT
      IMPORT COPY CATALOG
      EXIT GROUP
      INSTRUMENT CFGS.
      PASTE CATALOGS
      GROUPS
      INSTRUMENT CFGS.

      Menu strip options may act on both items in the left hand side column as well as items in the main editing window, and are grayed and striked out if the item is not active/highlighted (e.g., the catalog instead of the group). The icon menu was introduced in the previous chapter. Here the menu icons behave exactly the same as in the SCT.  The fly-over tool-tip help will remind you of their actions.

      3.2.2. Spectral Line Resources

      Creating a spectral line resource is similar to creating wide band resources as outlined above, except for the more advanced specification of the subbands and subband frequency tuning and possible Doppler setting of the frequencies.  Eventually, resources with the requested correlator settings will be pre-filled from information submitted to the PST during the observing time allocation procedure.  However, at this stage not much of this has been implemented.

      The NRAO Defaults resource catalog contains full polarization dual IF pair spectra-polarimetry resources (the wide band continuum resources). If they appeal to you, you can copy/paste them in a personal catalog just as for the wide band resources above and edit them as needed. Check the spectral line resource properties very carefully as the spectral line resources in the NRAO Defaults have a fixed sky frequency whereas you probably want to use a rest frequency in combination with Doppler setting.  Most likely, however, you will opt to create your own resource from scratch, just like creating a wide band resource previously.  Some items that need extra attention are described below, step-by-step, but first a small detour to outline the options for creating large numbers of narrow frequency channels.

      Recirculation versus Baseline Board Stacking

      Spectral line observations are typically constrained by the requirement to have the best spectral resolution (i.e., narrowest spectral channel width) combined with the best velocity coverage (i.e., widest observing bandwidth), the latter perhaps also for calibration purposes (as gain calibration is done per subband).

      The maximum subband bandwidth is 128 MHz and can be decreased by factors of 2 to 31.25 kHz(*). Total bandwidths wider than 128 MHz are achieved by placing subsequent bandwidths next to each other with the caveat that the few channels next to a subband edge should be considered lost for line work (on either side of the boundary, for continuum work as well). To obtain a contiguous bandwidth which is near-homogeneous in sensitivity and without any subband boundary gaps, another baseband would be placed some MHz offset (e.g., half a subband bandwidth) from the original baseband to enable subband stitching in post-processing. Note that this limits the number of available basebands for other line settings.

      A single Baseline Board Pair (BlBP), out of 64 available BlBPs, can handle 256 spectral points divided over the polarization products (polProd). That is, it can deliver 256 spectral channels in single polarization, 128 spectral channels in dual polarization, or 64 spectral channels in full polarization. The channel width (which is slightly less than the spectral resolution) is then simply the subband width divided by the number of spectral channels.

      With one BlBP per subband as standard, the selected subband bandwidth is thus limited to 256/polProd channels which may not be narrow enough to achieve the desired spectral resolution. There are two ways to overcome this limitation: Baseline Board Stacking uses more of the limited amount of hardware and Recirculation uses limiting the total bandwidth per subband and CPU cycles. Both have their disadvantages and the choice depends on the science requirements. If either can be used, we recommend using Recirculation.

      Baseline Board Stacking uses additional BlBPs to compute extra channels in a subband (of any width up to 128 MHz). Each additional BlBP increases the number of spectral channels by 256/polProd. As there are only 64 BlBPs total, and as every subband uses a minimum of one BlBP, Baseline Board Stacking reduces the number of subbands that can be observed to less than 64, and in the extreme case to a single subband of 128 MHz or less. When most of the 64 BlBPs are being used and all of the subbands are required (instead of some being recognized as less important and thus "desired" versus "required"), the observations will not take place if one or more BlBPs are inoperable. The 3-bit NRAO default setups use 64 BlBPs with the subbands at the baseband edges "desired" to allow continuation of operations when not all BlBPs are available.

      The Recirculation option uses software to compute extra channels. For this, CPU cycles are "freed up" by limiting the subband bandwidth fed to the BlBP to less than 128 MHz to obtain more lags (in factors of two), running the data through the board for a second, third, etc., time; hence Recirculation.  As subband bandwidths (and CPU cycles needed to process them) can be decreased by factors of 2, each halving thus allows a doubling of the number of channels in the subband, currently up to a factor of 64. This does not require additional BlBP hardware and thus retains the possibility of using all subbands, albeit at less subband and less total bandwidth. Currently, subbands of 128 MHz must use Baseline Board Stacking to achieve more than 256/polProd channels.

      Baseline Board Stacking and Recirculation can be used simultaneously in the same subband (if less than 128 MHz), and configurations with multiple subbands configured with either or both are allowed. Note that here a correlator setup can still request all 64 BlBPs and thus designating some subbands as "desired" is still highly recommended, but Recirculation gives the option to use less than 64 to achieve the number of spectral channels.  However, requesting a large number of channels, whether or not with Baseline Board Stacking and/or Recirculation, yields higher data rates than normal with the default integration times. To remain within the limits set by the observatory, longer integration may be needed which has an impact on time averaging smearing in the larger array configurations and thus on the field of view.

      The choice for one or the other, or even for less channels than anticipated, depends on the trade-offs that can be made for the science goals and remain a responsibility of the observer.

      (*) When observing at such narrow subband bandwidths it is good to check with the NRAO helpdesk. There are other operational constraints, in particular the F-shift in bringing down the baseband, that need to be considered and that may decrease the usable subband bandwidth to much more than a (symmetric) few channels compared to the general case described above.

      Creating a new Resource

      First, navigate to the Resource Catalog Tool (RCT).  Then:

      • From the top menu strip, select FILE - CREATE NEW - CATALOG or select an existing personal catalog.
      • Your new catalog with the default name [New Catalog] appears in the main editing window. Change the name of the catalog to something useful (to remind you of its purpose).
      • Optionally add the names of co-workers who you want to share the catalog resources with and can edit the resources in the catalog.
      • At this stage you can opt to group your resources. This is not necessary, but convenient if you are going to have many resources. If you want to group resources in this catalog, select FILE - CREATE NEW - GROUP, and name your group under the Properties tab.
      • From the top menu strip, select FILE - CREATE NEW - INSTRUMENT CONFIGURATION. You will be presented with a resource page an example of which is shown in Figure 3.8 below.


        Defining the newly created Resource

        The instrument configuration is built up by going through 6 steps, represented by the 6 tabs in Figure 3.8, and summarized in the table below. If you know what you want exactly, e.g. because you have a fixed (sky) frequency for your line or have calculated your Doppler frequency by hand and want to include that in a fixed frequency resource, skip the Line and Line Placement tabs and tune the basebands (with Doppler setting switched off) and subbands directly in the Basics, Basebands and Subbands tabs. Before continuing you may want to read up on Doppler Setting and Dynamic Scheduling.

        TabFunction
        Basics Name resource, specify band and integration time
        Lines Enter all lines and their properties that you'd like to cover
        Basebands Tune basebands to opimize your line coverage
        Line Placement Generate template subbands to cover the lines
        Subbands Inspect subbands from previous step and modify if necessary
        Validation Validate for correctness

         

        Basics

        • Choose a correlator visibility integration time; the default integration times are given here, where the larger values will reduce the size of the data set. The correlator integration time may be adjusted later (upward) to remain within the maximum data rate for the specific setup you are creating.

        Figure 3.8 - Screenshot of the RCT in the 8-bit case, Basic Tab.  Note the two independently tunable basebands.  The 3-bit equivalent has four such basebands

        Lines

        • Specify the sky position for which your observations should be Doppler set (tracked); you can use the Import Source Position button to use a predefined source from one of your source catalogs in the SCT. Note that any velocity specified for a source is not used in the resource; this is specified here in the Lines and Baseband tabs. If you have more than one source, you can specify an average velocity, a separate line for each source velocity or create a new resource per source. Do not specify a position if you are specifying an exact sky frequency for your lines.
        • In the Lines table, click on Add Line. A row with label L1 will appear. The next step is to specify the specifics of the subband that will cover this line.
        • Name your line and specify the line rest frequency, line-of-sight velocity at which the line should be observed and the rest frame and convention to be used in Doppler calculations. Furthermore, specify the minimum velocity range that should be covered. Note that a first order bandwidth for this range will be calculated using the line frequency and displayed below the input field. This will set the subband bandwidth to the next wider possible value. Try to keep the bandwidth for the range as narrow as possible for your science to maximize flexibility in placing the 128 MHz boundaries between your anticipated subbands; you can widen them later. In general pre-defining subbands wider than 32 MHz will often give problems in the initial placing of the subbands as the final baseband center frequencies are not well determined. Similarly the (maximum) channel separation input field will display the velocity width converted to frequency below the input field, and set the channel separation in the subband to the next possible narrower value. Finally choose the polarization products required for this line. By default the option to use Recirculation when possible (over Baseline Board Stacking) is switched on, and unchecking the box will consider Baseline Board Stacking only when configuring the subband for this line setting.
        • Build your list of lines by adding additional lines and repeating the previous step. You can copy the last line to copy the items and make your editing easier using the Copy Last Line button. If there is a specific frequency that you want to Doppler set (track) on, but is not a line that you want to observe as such, e.g., a baseband center frequency, include it in this list. To remove an unwanted line click the delete icon (delete) to the right of the row that needs to be deleted.
        • Note the summary of the baseline board pairs (Bl.BPs) in the top table next to the baseband graph. Only 64 baseline board pairs can be used and this number will be updated in the following steps when generating and updating subbands.

        To prevent having to do the work again for a next resource with similar lines there is an option to download or import the line details at the bottom of the lines tab. See Section 6.5 in the OPT manual for the syntax.

          Figure 3.9 - The Line Tab of the RCT after adding two lines.  Note how neither baseband covers a line

           

          Basebands

          • For the high frequency bands (K, Ka, and Q) the default is to use 3-bit samplers covering 8 GHz bandwidth using four 2 GHz basebands, but you may select the 8-bit system to use two 1 GHz basebands. For all other bands the default is to use the 8-bit setup. If 3-bit selection is not possible, copy (and edit) a resource from the NRAO Defaults catalog. Ignore the message that there are no subbands defined yet (which is done in a next step).
          • For each baseband select the baseband center frequency if the defaults won't work for you. Remember that the exact baseband center itself cannot be observed as it falls on one of the 128 MHz boundaries. Try to place your lines as much as possible in the middle of the available basebands, or alternatively in as few basebands (i.e., one if possible) as long as your lines are not very close to the baseband edges and not close to the 128 MHz intervals within each baseband. If you plan on doing this, remember the restrictions: for 3-bit the baseband centers for A1C1 and A2C2 must be well within 2.5-3 GHz (same for B1D1 and B2D2) to pass through the 5 GHz down-converted frequency bandwidth at the antennas. In cases where AC and BD are spread over a large range (>4 GHz) usually AC needs to have the upper center frequencies and the maximum span of all frequencies in any band must be less than 12 GHz. Ka band has extra restrictions (see below or the OSS).
          • Once the baseband centers are set, typically after the subband step below, select for each baseband the Doppler setting characteristics. That is, from the list of lines specified in the Lines tab define the line that will be used to calculate the Doppler shift of the entire baseband for the sky position entered in the Lines tab. Formally your Doppler frequency will be correct for only one line per baseband at the start of your observation, but in practice the differences between the lines in a baseband usually are small enough to correct for in post-processing. This Doppler setting "line" does not have to be observed as that line, but it needs to be specified as a line option (with velocity and definitions) in the Lines tab. For example, one can specify a pseudo-line which is the baseband center frequency, skip generating a subband for it (as that won't fly because it falls on a 128 MHz boundary), but select it as the Doppler setting frequency.

          Figure 3.10 - The Baselines Tab of the RCT after shifting both basebands such that both lines are covered

           

          Line Placement

          • The lines you specified earlier will show up in a summary table. For each of the lines you want to observe hit the Generate button, which will pop-up a dialog window for confirmation. This will generate a subband with a subband bandwidth which covers at least the velocity range requested, with enough baseline board pairs assigned (within the recirculation factor allowed). It aims to cover the bandwidth with spectral channels that are at least as narrow as the requested separation with the specified polarization characteristics. When created, the part of the baseband around the line will be shaded lighter to show the allocation in the baseband (though it may be too narrow to be distinguished). If a line can be observed with more than one baseband, there is the option to select the baseband. If you hit the Generate button more than once you will generate identical subbands without actually increasing the sensitivity for that line.

          Figure 3.11 - The Line Placement Tab.  Clicking Generate creates a suggested subband setup which can be inspected in the following tab: Subbands

           

          Subbands

          • Every baseband tab will now show a table with the subbands that were generated during the Line Placement step which covers each individual line. The color assigned to a subband indicates which of the four correlator quadrant's baseline board pairs are assigned to it (in continuum typically 16 subbands have the same quadrant color) and currently for 8-bit setups you may generate up to 32 subbands in either baseband.  You have the freedom to modify the subband bandwidths, but note that each doubling of the bandwidth requires a doubling of the number of baseline board pairs or recirculation factor to retain the channel frequency width (the default behavior is to keep the number of baselineboard pairs and recirculation constant, doubling your channel separation with each doubling of the subband bandwidth). Changing the number of polarization products has a similar effect. If subband bandwidths of less than 128 MHz are used, enable Recirculation to reduce the use of the limited amount of baseline board pairs (see above).
          • The Snap to Grid and Fix to Baseband checkboxes are unchecked and/or checked by default, depending on the situation. Unchecking Snap to Grid allows for using more correlator resources to define a flatter bandpass filter and unchecking Fix to Baseband keeps the subband tuned if you decide to recenter the baseband respectively. For now, the best option is to keep them with the default at generaton: both unchecked for line work and both checked for subbands intended as continuum. Note that these items are tools to figure out the best placement of the baseband center frequency for your lines and do not really do anything during the observations and will be ignored after the frequencies are defined.
          • Under every baseband-tab (i.e., repeat this four or two times) you want to make sure you have enough continuum sensitivity (subband frequency coverage) to be able to calibrate your gains. You would want to include extra subbands you can use for this by clicking Add/Fill Subbands and placing them in a part of the observing band away from strong lines; whether they are your bright targets or RFI (for 8-bit samplers you may only generate 32 subbands). Each defined subband will fade a fraction of the color of the baseband in the graph on top so you can see whether they are avoiding your line. By default these subbands have the Snap to Grid and Fix to Baseband options reversed compared to the subbands containing your lines for flexibility.
          • If you are unhappy with any of the subbands you can delete individual subbands with the delete icon (delete) at the right hand side of the subband table. Multiple subbands can be selected and deleted with the Delete Selected Subbands button.
          • Subbands can be changed individually, or be selected and bulk-edited using Bulk Edit Selected Subbands. Note that editing is limited to the current baseband tab only; if you, e.g., want to change the polarization of the whole observation you have to repeat the editing in each of the baseband tabs. You can only enter the center frequency for subbands of 16 MHz and narrower, provided that they do not cross a 128 MHz boundary; wider subbands can only be selected from a fixed drop-down list.
          • You may limit the number of subbands (i.e., less than 64 total, 16 per baseband) in favor of more correlator products in another subband. The number of correlator products in a baseband is the number of spectral channels × the number of polarization products and each baseline board pair can produce 256 products. Doubling the number of baseline board pairs doubles the number of products at the cost of a subband per baseline board pair, but see above how to counter that with Recirculation. Keep an eye on the total number of baseline board pairs used in the top table (next to the graph); only 64 baseline boards are available. Also make sure that you do not exceed the maximum data rate (25 MB/s) for the sum of all subband resources.
          • If you want to start anew (using the already specified baseband centers), click Clear All Subbands to remove all subbands in all basebands, or delete the resource (or Group, Catalog) completely using the menu strip or icon menu.
            • Finally, judge the subbands: can they be merged, are they too close to a 128 MHz edge, are there left-over resources (baseline board pairs) to include more (e.g., continuum) subbands, to double the number of channels to increase the spectral resolution for one or more subbands, etc.?
            • The automatically generated subbands are made on a best effort basis; check the output!
            • When a subband is very close to a 128 MHz baseband edge (hover with your mouse over the yellow triangle to see how much), you may want to shift the baseband in question to a new center by returning to step 2; when doing so you should not have (any of) the generated subbands fixed to the baseband so they will not stay fixed close to the 128 MHz edge of the baseband (the default for "Fix to Baseband").
            • Adding 128 MHz continuum bands and/or switching on Doppler setting should be done after the baseband center frequencies are determined.
            • Each doubling of the subband bandwidth (e.g., when merging subbands seems useful) requires a doubling of the number of allocated baseline board pairs to retain the channel width originally requested.
            • Changing the individual subbands invalidates the input given earlier; in principle no information stays correct when stepping backward but more lines can be added to step 1 and be generated in the following steps when baseband and subband centers were calculated previously.
            • If your science has the flexibility, assign some subbands a priority other than "Required". This will allow a scheduling block with this resource to run on the telescope even if some of the hardware is inoperable or if one or more baseline boards cannot be configured at the cost of missing those subbands. The larger the number in the label, the less desired a subband is in case there are more choices that can be traded off. That is, the subband with the highest desired-number (64) will be left out first if such a need arises, the lowest (1) last, but Required subbands are never skipped.

            Figure 3.12 - The Subband Tab of the RCT, in this case showing baseband A0/C0. Note in the bottom panel where the selected bandwidth falls in the baseband

             

            Validation

            • This allows you to inspect your setup in terms of frequencies and correlator resources (i.e., baseline board pair allocations). Check your resource, from top to bottom. If you create more than one resource, check each of the resource properties using the Show/Edit icon for each catalog entry. You can also reorganize your resources by adding groups (FILE - CREATE NEW - GROUP) and by moving your resources around using the column icon menu, or using EDIT in the top menu strip. Unwanted resources can be deleted using Cut.
            • If you are unhappy with the name of the catalog or group you can always rename it by highlighting it and then clicking on the Properties tab.

            If there is a need to modify the existing resource, after generating a resource and attaching it to scans in a scheduling block in the OPT, rename or copy it to a new name and make the modifications in the resource with the new name. This adjusted resource has to be re-attached to the scans in the scheduling blocks, replacing the faulty resource. The easiest way to do this is with the Bulk Edit Scans tab on the selected scheduling block. Having a different name for the two resources is extremely useful in checking whether the edit was successful and whether scans with the old resource have been overlooked.

            Final Check

            After all this data entering, make sure you check your catalogs for correctness. It is important that your frequencies (with Doppler definitions) are correct before creating scans in the OPT, and before storing to disk or sharing your catalogs with your collaborators.

              3.3. Specific Resource Details

              The previous subsections on resources were dealing with resources defined to do the scientific astronomical observations you proposed for. However, to get the most out of your data, it sometimes is helpful to add some specialized scans to the SB in order to optimize the observations or to aid in the calibration of the instrument. Typical for high frequency (higher than ~ 15 GHz) are pointing scans and tipping scans. The observing mode for such scans (pointing or tipping) is selected at the scan level in the OPT. For pointing scans, typically one would use resources that are different from your scientific observation resources, e.g., a different bandwidth, correlator setting, or even a different observing band. We have added some of these resources to the NRAO defaults catalog, available to the OPT at the scan level or to copy/paste to your personal resource catalog.

              Pointing scans are used to improve telescope pointing accuracy which increases the sensitivity of the observations. As the instantaneous telescope pointing is only accurate to several arcseconds, this error may become a considerable fraction of the primary beam at high frequencies. Solving for this error is done using primary pointing scans on a strong source at X band, after which a secondary pointing may be performed at the observing frequency if deemed useful (the pointing resource in C band is not recommended). The actual pointing action is selected as Interferometric Pointing under scan mode in the scan details (see OPT), which may use the resources named Pointing presented in the Pointing setups resource group in the NRAO defaults resource catalog. It is important to use these pre-defined setups as they typically use a different frequency, bandwidth and integration time than the other (default) resources.

              Tipping scans are used to obtain a measurement of the atmospheric opacity at high frequencies, which allows for an estimate of the loss of sensitivity due to absorption of emission from the source of interest by the atmosphere. The actual telescope tipping action is selected as Tipping under scan mode in the scan details (see OPT). Because you typically want to do tipping scans at your observing frequency you would either use resources from the NRAO defaults catalog or you would reuse your own resource at the frequency you want; no new resources are needed. Tipping scans are currently disabled.

              Resources at Ka band: There is an issue with specifying the frequency of IF pair AC at Ka band. That is, tuning any part of the AC IF pair band below 32.24 GHz will not result in valid data, regardless whether this is A0C0 or any of A1C1 or A2C2. Only the BD IF pair can be tuned to frequencies below 32.24 GHz; use the BD IF pair instead of AC IF pair when you only need one IF pair for your resource with a frequency tuning below 32.24 GHz. If the OPT web application validation detects that any part of the bandwidth of IF pair AC is tuned below this 32.24 GHz it will try to swap the AC IF pair with the BD IF pair. If this is not possible, it will issue an error (in red font) in the interface feedback strip if this frequency is specified as a fixed sky frequency. It will issue a warning (blue font) for rest frequencies, as the particular tuning depends on the details of observing date, telescope pointing direction and source velocity definitions. Note that a rest frequency above 32.24 GHz may shift to below 32.24 GHz once it is assigned to a scan in the OPT. This should give you an error in the OPT; you should be aware of this possibility and pay attention to this. However, it is better to assign IF pair BD to the resource if you anticipate this might happen, if you still have this freedom in your resource of course.

              When observing very close to 32 GHz with both IF pairs, some combinations where frequency coverage of AC and BD are overlapping are not possible. Consult Helpdesk for options, preferably before submitting the proposal.

              The very wide bandwidth of the Ka band receiver, from 26.5 to 40 GHz, would suggest that IF pair separations of up to ~13 GHz are possible. Restrictions in the signal path, however, limit this separation to 10 GHz. The OPT web application validation will issue an error if the separation between IF pairs AC and BD is more than 10.5 GHz in sky frequency (with IF pair AC tuned to have the higher frequency centers). A separation of more than 10.5 GHz in rest frequency will result in a warning as, e.g., highly red-shifted lines may end up with less separation when the actual sky frequencies are calculated.

              Resources at K and Q band: If you choose the RF signals in the different IF paths to be separated by a large amount, it is possible that the OPT will only let you create a resource where the baseband frequency center(s) in IF pair AC is higher than the baseband frequency center(s) in IF pair BD, similar, but the reverse of the Ka band restriction above.

              4. Using the Observation Preparation Tool (OPT)

              4.1. Orientation

              Assuming you already have successfully logged in to the OPT web application, and assuming that there is no message in the "Important message banner" that makes you decide to abandon the OPT for the moment, look for the navigation bar at the top. If "Observation Preparation" is not in bold face, but in normal font and underlined, click on it (Figure 4.1).

              Figure 4.1: Web browser screen shot of the OPT opening page.

               

              A short introduction to the layout of this tool's page has been given in the introduction (Chapter 1). This chapter uses the information contained in the resource catalogs (Chapter 2) and information contained in the source catalogs (Chapter 3). It is assumed that the contents of these chapters are familiar, and that the information in the (re)source catalogs is correct. There should be at least one project tree visible in the project browser, with a PB, and possibly a SB and a scan. To activate your project (i.e., to load it in memory), click on it and expand the branch by further clicking on the plus sign (\includegraphics[height=3mm]{psimg/expand.png.ps}) in front of its name. Do this for the project that you want to be working on. This may take a while if there are many SBs and/or many scans in the SB(s). As with every operation in the OPT web application, please exercise patience.

              If you need to define an additional (test) project or if your project was not filled from the PST, use FILE - CREATE NEW - TEST PROJECT. This should create a new project tree that you can name and edit, try out some ideas, etc..

              The purpose of the OPT is to combine a source from one of your source catalogs with a resource from one of your resource catalogs, and to specify an observing mode, a time interval and an intent for this combination. Repetitive combinations will build an observing schedule that defines a SB observation which may be executed by VLA operations. The sequence of scans in a SB will show in the left hand side column in the project (etc.) tree.

              It is useful to outline the project in terms of the PB and SBs in advance. Use information from the proposal, etc. (see Chapter 1) and create (re)source catalogs with only the subset of (re)sources that will be used in the SB you are about to create. Having your (re)sources in small personal catalogs is convenient and faster than having large catalogs or switching back and forth between your personal catalog(s) and, e.g., the "VLA" catalog . Also consider exporting and removing (in that order!) all other (re)source catalogs and projects that you don't need. Check the remaining (re)sources for correctness before you continue.

              The left hand side column

              in the OPT contains a collection of projects. Projects are subdivided in a tree of PBs, each subdivided in SBs, which each contain scans and/or loops of scans. This column, per SB, thus holds the scan list, i.e., the column represents the observing schedule. In contrast to the RCT and SCT, much of the editing in the OPT will be performed in the left hand side column as well as in the main editing window.

               

              The icon menu

              in the OPT has more options than in the RCT and SCT. The common icons have the same functionality as the icons in the RCT and SCT, but as more editing is done in the left hand side column some extra icons (with their fly-over help tool-tip) are added. Only icons valid for the selected or highlighted items (e.g., PB or scan) are displayed. A full list of icons and their meanings is shown in the listing. These icons do not apply to the main editing window, only to the Project tree items.

              Click to allow multiple selections for cut/copy/paste
              Add a new (blank) scan
              Page Add Add a new scan (with copy of source and hardware only)
              Cut Cut (delete) selected tree item
              Page Copy Copy selected tree item
              Page Paste Paste selected tree item
              Separator Icon menu separator (no action)
              Arrow Up Move selected item up by one in current tree level sequence
              Arrow Down Move selected item down by one in current tree level sequence
              Arrow Left Promote selected item up, above the current tree branch (out of loop)
              Arrow Right Demote selected item down, in the next current tree branch (into loop)
              Separator Icon menu separator (no action)
              Collapse All Collapse/hide all items in the selected tree
              Expand All Expand/show all items in the selected tree

               

               

              The menu strip

              options in the OPT are a bit more complicated and at this time some of the options are disabled or non-functional. The options that are currently relevant in creating your schedule are given in the table.

               

              FILE CREATE NEW TEST PROJECT EDIT
              VIEW
              HELP
              PROGRAM BLOCK CUT [ITEM NAME] HIDE/UNHIDE PROJECTS ABOUT THE OPT
              SCHEDULING BLOCK COPY [ITEM NAME] ABOUT ME
              SCAN PASTE NEW FEATURES
              SCAN LOOP TO DURATIONS DOCUMENTATION
              SUBARRAY UNROLL LOOP CONTACT SUPPORT
              REFRESH PROJECT
              IMPORT PROJECT...
              IMPORT SCHEDULING BLOCK...
              IMPORT SCANS...
              EXPORT PROJECT
              EXPORT SCHEDULING BLOCK
              EXPORT SCANS
              EXPORT CATALOGS...
              EXIT

               

              Figure 4.2: Web browser screen shots of the SB details page, top portion.

              4.2. Defining Your Project's Program Block and Scheduling Block(s)

              There should be at least one project in your tree (if not, use FILE - CREATE NEW - TEST PROJECT). When you expand it using the plus-icon in the icon menu, a PB, and possibly a SB and a scan would be present. Click on your project and give it some descriptive title if it has not been filled in from the PST information. Similarly, click on your PB and name it.

              Each PB is defined for an observing trimester, typically a single VLA array configuration or "Any" configuration. For your PB, if not transferred from the PST, select the array configuration for which this PB is valid by dragging the array configuration name from the right hand side column to the left hand side column. More than one (consecutive) array configurations, or "Any", can be specified. If your project spans more than one clearly different observing runs per trimester, e.g. some southern sources in A array and some more northern sources in B array, simply add more PBs to this project using FILE - CREATE NEW - PROGRAM BLOCK. The table at the bottom is a read-only, sortable administrative table. It keeps track of the total time scheduled in the SB(s) in this PB.

              Create a first SB if necessary: FILE - CREATE NEW - SCHEDULING BLOCK. When you next click on the SB, you are presented with six tab-pages in the main editing window (Figure 4.2). In the first tab ("Information"), name your SB and select whether it is a fixed-date SB or a dynamic SB - the tab-page will change with different scheduling constraints depending on the choice made; they should have self-explanatory labels and fly-over help tool-tips.

              Figure 4.3: Web browser screen shots of the SB details page, bottom portion.

               

              For fixed-date allocations you may have to fill out the starting day (VLA day, i.e., modified Julian day number on the VLA schedule) and LST time of your allocation. To schedule in UT time, e.g., for VLBI scheduling, you can use the UTC radio button. The "Array Starting Position" is an option to aid you in anticipating a worst case scenario of the antenna wrap, or to calculate the slew time in the unlikely case that you know where the array will be pointing at the end of a previous observation.

              For dynamically allocated observing time you are asked if there are any scheduling constraints. Possible constraints are a range of possible (or convenient) LST starting times, and a first date of possible observations. Other constraints deal with the weather at the site. Defaults for weather at specific bands are given in the table; see Figure 4.3. Select the description of the weather constraints that you want to apply, or specify your own constraints (supply both wind and atmospheric phase limits). The antennas will stow when the wind speed reaches 18 m/s). Consult Appendix A for more on SBs for dynamically allocated observing time.

              This tab-page also contains a field in which you can communicate your notes, requests, concerns, other constraints, etc, to the operator. If your observations for this trimester include sources that cannot be observed in one consecutive time interval in the time allocated, or if you have more than one fixed-date allocations, you can define different SBs for the different LST ranges or fixed-dates, again by using the menu strip at the top: FILE - CREATE NEW - SCHEDULING BLOCK. If your observing runs are identical increase the repeat count or, if they are very similar, alternatively copy the SB and adjust the new SB as required.

              You are now ready to start making scans in this SB.

              4.3. Building Your Scheduling Block Scan List

              The idea is to define a sequence of scans in the left hand side column, each with a source, a resource, an observing mode, a time interval and some reason (intent). Each time a scan is added you need to specify these items. However, it is not always straightforward to assemble this scan list in the sequence you want the first time around, and you will need to move scans around. This is easily done! That is, there is no need to panic if you make scans (a bit) out of order; it is almost straightforward to add, e.g., an extra bandpass calibration scan, to move some scans to the middle of the observation, or to redefine source loops after the main framework of your schedule is set up.

               

              The First Scan

              Create a first scan if necessary: FILE - CREATE NEW - SCAN. Select your first scan (click on "[New Scan]" next to the telescope icon and "STD" in the left hand side column); it contains default parameters such as a scan mode "Standard Observing" for 5 minutes "Duration (LST)". The number of tabs at the top depends on the scan mode. Current scan modes are "Standard Observing" (tracking a sidereal position in the sky), "Interferometric Pointing" (for improving telescope pointing), "Tipping" (for measuring opacity curves; not currently in use), "Holography" (for measuring antenna response; internal NRAO use only), and "On The Fly Mosaicking" (for taking data in a constant slew that is different from compensating for Earth rotation). Each mode has a different code that shows next to the telescope icon: STD, IP, TIP, H and OTFM respectively. Next we will describe "Standard Observing" (STD). IP and TIP modes will be described further below; OTFM mode is described in Chapter 5. Be sure to also check the requirements for setup scans and intents as described in the attenuator section of the Guide to Observing with the VLA.

              Selecting Standard Observing (STD) for "scan mode" displays two tabs: "Overview" and "Comments". In "Overview" you set up the actual scan (Figure 4.4), whereas in "Comments" you may enter anything specific for this scan for your own reference.

              Within the "Overview" tab two tables are displayed. In the first, you name your scan. Note that the scan name is just for the scheduling display in this tree (and in the summary); it is the source name specified in the SCT catalog that ends up in your data. It is followed by scan mode ("Standard Observing"), the antenna wrap, whether or not you want to apply the solution from a previous pointing scan, and whether observing "over the top" is acceptable (most likely not!). Also the "Phase & Delay Cal" and "Record On Mark V" are for specialized scans (VLBI and Pulsar observations) and should not be used (i.e., should be left unchecked) for standard observing! The antenna wrap and reference pointing are described further below.

              The second table contains the actual target source, the hardware setup (with Doppler tracking settings), scan timing and intents with this scan. Each of these fields must be completed, and an error would result if any of these fields is unspecified.

               

              Target Source

              The "target source" column either shows you the name of the target source (i.e. telescope pointing direction) or tells you that no source is assigned. A source needs to be specified and if it is not the one you want, press the "Import" button. This brings up a dialog box to interact with the source catalogs that are in your SCT database. Select the source catalog and the group within that catalog from which you want to extract a predefined source. Simply tick the source name - you may have to scroll down your list to find the desired one. Note that you cannot define sources "on the fly"; only sources specified previously in a source catalog in the SCT can be selected. You may need to switch to the SCT if you desire to observe a source that was not previously defined and do so at this time.

              Figure 4.4: Changing the resource in a scan overview/details page.

               

              As you will be doing this changing of sources potentially for every scan, you probably see that it might be useful to collect all sources that you want to use in this SB in a single catalog (group), i.e., with your target sources but also with your calibrator and tipping sources from, e.g., the "VLA" list. Otherwise you will be switching back and forth and scrolling up and down a lot.

               

              Hardware Setup and Doppler Tracking

              The "hardware setup" column is very similar; it shows the hardware setup selected if a resource was previously assigned. Click "Keep Previous Conf." to select the exact resource setting of the preceding scan (it must be defined for that preceding scan of course). Click "Import" to get a familiar dialog box to select your resource catalog, resource group and resource from (only) the predefined resources in the RCT. Resources cannot be defined "on the fly". Also here it is useful to specify all hardware resources (and pointing scan setups) in this SB in a single resource catalog (group), but because resource catalogs typically are not as extensive as source catalogs it is less of a hassle if you don't.

              Spectral line resources that were set up with a rest frequency instead of a fixed sky frequency have to be specified with an option for the Doppler Setting in the RCT! The recalculated sky frequencies for the LST starting time and LST starting date of the SB as specified in the Reports page will show in the scan listing mentioned further down.

               

              Scan Timing

              The scan timing determines the length of the scan, either in LST (sidereal) or in UT. The difference is about ten seconds in an hour. You must keep your schedule in LST duration when observing with the VLA only. Options are to set the exact time the scan has to end ("Stop Time", only useful for fixed date schedules), the total (maximum) time the scan may take from the end of the previous scan including telescope slewing time ("Duration (LST)"), or the time the telescopes should track the source regardless of telescope slewing time ("On Source (LST)"). Dynamically allocated observing time schedules must be in "Duration (LST)". It is possible to create schedules in On Source time to investigate slew times between sources, etc., but the SB must be converted to LST duration prior to submitting. This is done best by picking a sensible LST start time in the Reports page, clicking "Update" to recalculate the slew times and to make use of Edit-To Durations selection from the menu at the top.

               

              Scan Intents

              In the intents you should indicate the intent of the scan. By default it is set to "Observe Target" (for "Standard Observing"), but you can add more than one intent to it. For example for your phase calibrator you would tick "Complex Gain Calibration", for 3C286 you would choose "Flux Calibration" and for any suitable source you intend to use for bandpass calibration you would select "Bandpass Calibration". The most common options are shown, and the more specialized options that you probably would not want to use are hidden behind the "More" button. More than one intent may be ticked, and will be useful in particular for the automated calibration pipeline. Note that if you leave the intent to the default (Observe Target), you will not have calibrator codes with your data which may complicate your data reduction; in particular it will prevent the automated pipeline from processing your data. On the other hand, the current practice of having to schedule "dummy" scans that take care of setting up the hardware (frequency tuning, local oscillators, attenuators, etc), usually do not contain useful scientific data. We now have an intent labeled "Setup Intent" that should be chosen for such scans so that the pipeline knows to skip this data during the data reduction.

               

              Comments Tab

              Write anything you would like here; it is a comments and notes field for your own reference.


              Subsequent Scans

              There are a few ways to add extra scans. A blank-slate scan can be obtained using the menu strip: FILE - CREATE NEW - SCAN. The options are to place it before or after a selected scan, or in a selected loop.

              Another way to obtain a new scan is by using the icon menu. It has several icons dealing with creating scans. Using the icons for copy and paste, a new scan can be created from a previously created scan, and be pasted at any position in the scan tree after selecting (highlighting) the scan it has to follow or precede in the tree. The same can be achieved using the icon with the little green dot (\includegraphics[height=3mm]{psimg/page_add.png.eps}), which will paste a new scan directly after the scan that is copied. Useful when building your scans sequentially.

              You probably want to change your source of the scan if you place the new scan directly after the previous one (otherwise it is the same scan). Please take an effort to fill out the correct scan intent for each scan.


              Calibration

              Most observers would want to include calibration scans next to their target source scans. Almost always you would schedule one or two scans on a flux density scale ("amplitude" or "primary") calibrator (e.g., 3C286, J1331+3030) somewhere in the schedule where it is convenient. Spectral line observers would also include one or more scans on a bandpass calibrator if the flux density calibrator is not suited for this (if it is, please select both flux density scale and bandpass calibration as "Intents" for this calibrator source).

              The target source position scan is typically sandwiched between complex gain ("phase" or "secondary") calibrator scans in order to interpolate the phase changes between the beginning and end of the target scan. If observing more than one frequency setting (resource) and switching between them within an SB, however, there is no guarantee that returning to the same resource the phase from a previous scan using that resource is preserved. That is, using more than a single resource regardless of the resources are within a single receiver band or not, might cause phase jumps when interpolating between the scans. Therefore, it is extremely important to bracket the target with complex gain calibrator scans that use the same frequency setting as the target to avoid experiencing any phase jumps.

              Because of the short coherence times at high frequencies and/or longer baselines and therefore the many calibrator-target source scan switches necessary, it is customary to do this using a scan loop between your calibrator and target sources to increase integration time beyond the coherence time.


              Scan Loops

              Setting up a "scan loop" is done using the menu strip: FILE - CREATE NEW - SCAN LOOP. It will show you a "Scan loop details" page in the main editing window; assign a descriptive name to it and specify the number of iterations of this loop. The tick-box for bracketed means to copy the first scan in the loop to the end of the loop, i.e., add another calibrator scan so that the last target scan is also bracketed between two calibrator scans when the first scan in the loop is on a calibrator source. The four tree setups of scans in the table of examples below are equivalent; they all enclose scans on a target with a scan on a calibrator source before and after each target scan, i.e., they all result in the sequence Cal - Target - Cal - Target - Cal.

               

              No LoopNormal LoopBracketed Loop
              Individual Scans two different orderings should start with Cal
              No Loop Loop 1 Loop 2 Bracketed Loop

               

              In the example on the right hand side (the most compact, bracketed loop) the double-star after the loop icon, in front of the number of iterations of this loop, indicates that this loop is a bracketed loop. To achieve bracketing of the target source(s) with scans on the calibrator source, the bracketed loop must begin with the calibrator source scan. Of course one is free in choosing any of the possible scheduling solutions; the resulting observing script is the same either way, but the scan listing summary will differ in compactness and clarity. Note that the first scan of a loop must have its own Resource; your SB will not validate if you attempt to set "Keep Previous Conf." in the Resource setting for the first scan of a scan loop.

              A loop can contain any number of sources, not necessarily only a calibrator scan and a single target scan. If your target sources are near in the sky and you can get away with a single calibrator for all of these targets you can group them in a loop with more than one, say four, target scans before returning to your calibrator. Keep in mind that the total loop time should be shorter than the anticipated coherence time at our observing frequency. Loops may also contain loops. If your loop is selected, adding a new scan will place this new scan in the scan loop. The only difference with a normal scan is that this scan will be scheduled as many times as the "Loop iterations" specified, consecutively in a loop with the other sources in the loop. When finished with defining a loop, you may want to highlight it and then collapse it (using \includegraphics[height=3mm]{psimg/collapseall.png.ps} from the icon menu) for a more compact display in the tree.


              4.4. Other Scan Modes

              Other scan mode options besides "Standard Observing" include "Interferometric Pointing" and "Tipping" scans, described in this section. These are special observing modes for calibration, typically applied when observing at high frequencies (above ~ 15 GHz).

              The other two modes are "Holography", which is used to measure antenna beam response and is for internal NRAO use only, and "On The Fly Mosaicking" mode, described in Chapter 5 of this manual.

               

              Pointing Scan

              (IP) may be needed at frequencies of about 15 GHz and higher (K, Ka and Q band). At these frequencies the antenna pointing accuracy (a few arcseconds) becomes a significant fraction of the primary beam. Observing with an inaccurate pointing thus may degrade the signal by a significant fraction. The antenna pointing is a function of the shape of the reflective surfaces and is influenced by, amongst other things, gravity and temperature. Therefore, observing at high frequencies may require regular pointing scans to determine offsets from the pointing model. These pointing offsets remain reliable for target sources within about 20 degrees in Azimuth or Elevation from the pointing position. Therefore, typically one would redetermine pointing solutions when moving to a different portion of the sky, or roughly hourly when tracking a (group of nearby) target source(s).

              Pointing scans are performed as a five-point raster observation on a strong (over 300 mJy) continuum calibrator, in first instance in X band continuum. This "primary reference pointing" scan usually yields sufficiently accurate pointing offsets, but if more accurate solutions are required a "secondary reference pointing" may follow at the (standard) frequency of the observing band. Secondary pointing is also performed in continuum mode (to be as sensitive as possible to the continuum source) in an attempt to improve the antenna pointing in the band of interest. However, local lore is that although this might improve the pointing a bit toward the pointing source, subsequent slews and with time passing by, this secondary pointing in general does not yield a long lasting improvement on the primary pointing. In addition there is the risk that for some antennas the secondary solution fails. The resources for secondary pointing scans are available, but it is debatable whether the extra time spent to perform a secondary pointing scan is worthwhile. Determining pointing solutions using spectral line sources, e.g., with SiO masers in Q band, has not been tested.

              Default pointing resources are included in the "NRAO defaults" catalog in the group "Pointing setups" for your convenience. You may want to copy the resources and pointing sources you wish to use from the standard catalogs to your personal catalog. Do not forget to select "Interferometric Pointing" for the scan mode and an "on source" time of at least 2.5 (LST) minutes. You want to start a block of high frequency observations with a pointing scan, and tick the "apply reference pointing" in the first tab-page of the scans in this block thereafter. This tick-box will actually apply the offsets that were determined in a previous pointing scan; if you forget you will be using the (most likely less accurate) default pointing model. Your very first scan may be a pointing scan, but as you don't know in what Azimuth the array starts, you want to allow for ample slewing time or anticipate a worst case scenario using the Azimuth starting conditions on the SB page.

              If the pointing scan has not finished by the stop-time of this scan, no valid solutions can be applied. If it has determined a pointing solution before the stop-time has been reached it will continue with another five-point raster, which may or may not yield new solutions (which will be averaged with the first raster solutions). For "secondary reference pointing" scans, apply the solutions of the preceding "primary reference pointing" scan.

              A pointing scan is for real-time calibration and, while very useful for real-time calibration, usually does not yield useful data for your project. The data is however included in the observations, be it that you need special switches to load the data in your data reduction package. You may study this data for reference, but the real-time corrections are already applied and cannot be undone.

               

              Tipping Scan

              Tipping scans are not currently supported - this section will be updated once TIP scans are being offered again.

              (TIP) may be needed if you are concerned about calibrating the absolute flux density of your target source(s). The atmosphere absorbs some of the radiation, and the fraction of the absorbed radiation depends on the opacity, the transparency of the atmosphere. It is mainly dependent on the content of water vapor between the target source and the antenna(s), and can be derived from a series of system temperature measurements at various elevations. One would redetermine the opacity on the time scale in which significant changes are expected, i.e., the time scale in which the water vapor content of the atmosphere above the telescopes changes. This is a strong function of baseline length and actual weather and no real guideline on time scales is available. Use common sense in the trade-off between overhead and usefulness of the scans in post-processing.

              Figure 4.5: Web browser screen shots of the SB scan listing page, top portion.

               

              Tipping scans are performed toward an Azimuth direction close to your sources at about the observing frequency. The scan samples seven elevations between about 20 and 60 degrees for a system temperature and can be directed from top to bottom (down) or from bottom to top (up). When you select an Azimuth for your tipping scan, be aware that shadowing may occur, especially in C and D array configurations. Avoid the Azimuth directions of the arms, i.e., avoid measuring tips close to the Azimuths of -5, 56, 115, 175, 236, 295, 355 and 416 degrees.

              You have to select "Tipping" for the observing mode to expose the tipping scan tab pages. Tipping scans are set up using one of your resources and probably are best done with the widest bandwidth available; make a new resource if you need it. You do not need a physical source. The "on source" time is fixed to 5 (on source LST) minutes, because it takes this much time to complete your tipping scan (in one direction, up or down). In the "Details" tab you will have to set the Azimuth and direction; do not forget this as otherwise you will be slewing to the default Azimuth of 0 degrees (North) and may hit a wrap constraint. It can consume half an hour of your observing time to return to your science observing. Always set the Azimuth.

              You may place any number of tipping scans anywhere in your schedule as you feel fit to monitor the opacity during your observations, although you may want to do this close to your block(s) of high frequency observations. Your very first scan may be a tipping scan, but as you don't know in what Azimuth the array starts, you want to allow for ample slewing time or anticipate a worst case scenario using the Azimuth starting conditions on the SB page.

              If the tipping scan has not finished by the stop-time of this scan, the data will contain those elevation samples (out of seven) that were completed. If it has completed the tip before the stop-time, it simply will continue with the next scan until the regular stop-time for that scan - this scan may be used to buffer the difference, e.g., absorb the extra time on your bandpass calibrator.

              A tipping scan is for off-line calibration and may or may not yield useful data for your project. The data is included in the observations and you need special switches to load the data in you data reduction package. A "tip" would allow you to determine the opacity of the atmosphere during the tipping scan (i.e., during your observation), and you can use that value to correct for the atmospheric absorption in your data. Read the manual of your data reduction package on how to obtain and apply tipping scan data corrections.

              4.5. Modifying a Scheduling Block and Editing Multiple Scans

              The schedule created may not be your most preferred schedule, both in the details of each scan and in the order of the scans. If you desire to rename a scan or a scan loop (or a SB or a PB), at any time select the scan and edit the name or time interval, or reselect a (re)source.

              Figure 4.6: Web browser screen shots of the SB scan listing page, scrolling further down to the bottom.

              By using the menu strip or the icon menu it is possible to delete, cut/paste and add any number of individual scans (or scan loops) to any position in the tree at any time. Some handy icons are the arrows that move a selected scan (or loop) up or down in the current tree (i.e., keeping loops intact as loops), and in or out of a scan loop. Currently still fragile, but useful, is to click the leftmost arrow (pointing to the "northeast": ) which allows to click multiple scans for copying or deleting. Always verify that the scan you moved ended up in the expected location. There seems to be issues with this feature if you are working deeper down in the left hand side column, i.e. in loops and loops of loops.

              Bulk Scan Edit

              It is not uncommon that an error is made in the resource, that one forgot to tick the apply reference pointing solution, or that one opts to use a different calibrator, etc. Note that for any (re)source definition change, e.g., a frequency, velocity or position, the new information has to be reattached to the SB. That is, changes made in the SCT and RCT do not propagate to existing scans in the OPT! For a simple scheduling block like the one shown above, a few clicks will allow to change individual scans quite easily. However, when a complicated schedule or many individual scan are affected, editing each and every scan is hard to do without making any mistakes during the process.

              If one uploaded the SB or scans with a text file, the easiest may be to edit the original file and upload that again, especially if that file is kept as a template or for future reference. Otherwise, one may use the Bulk Scan Edit tab of the SB to specify the parameters to change and the parameters to replace these with.

              As example below, consider the SB above where the K-band 8-bit line resource will be replaced by the K-band continuum resource. The steps to take are:

              • Navigate to the Bulk Scan Edit tab to be presented with a filtering page. Tick the checkbox in front of Resource and select, from the resources found in the SB, the resource that should be replaced (i.e., for the example here, K-band 8-bit).

              • Click the Select button at the top or at the bottom of the page.
              • In the replacement page that appears, tick the checkbox in front of Resource again. Now select, from the resources found in your RCT, the resource that should be used instead (i.e., K-band).

              • Click the Update button at the top or at the bottom of the page. The table will show the scans that matched the filter, the scans that had the original resource specified (note that it does not select scans with "Keep Previous Conf."), with the filter matches highlighted in yellow. In this particular case there are three such scans, the rest is using "Keep Previous Conf.".

              • If there are any changes you want from a "change all", uncheck the checkbox in the first column, in front of the scan name, that you do not want modified.
              • Click the Confirm button at the top or at the bottom of the page. The affected scans will briefly light up in the SB tree to show that the replacement has been executed.
              • Check one or more individual scans, and the information in the Reports page, that the changes have taken place. Note that it is much easier to spot if the new (re)source has a different name from before the change. Also, the new SB has to be validated again for, e.g., data rate and other properties that may have changed due to this Bulk Scan Edit.

              4.6. Checking and Submitting Your Scheduling Block

              This tab-page summarizes your SB in three tables. The first table displays all unique resources used in this SB, the second shows all unique source-with-resource combinations, and the third table lists the sequence of scans with their details. Obviously, you should check these tables thoroughly for each tiny detail, e.g., whether you applied the reference pointing solutions ("Apply Ref. Ptg.") to the scans where this correction is useful. The table with the scan sequence will show loops (if any) initially in a collapsed form. It is strongly advised to click the expand-icon (xpnd) to show the scan details of the scans in the loop. You can expand all loops in the scan table at the same time using the expand button in the top left hand side corner of the table, and similarly collapse all loops in one go. After verification that all these scans are as intended, the loop may be collapsed again.

              Figure 4.7: Web browser screen shot of the Validation and Submission page.

              Printing the SB information

              Note the "Use your browser's Print feature to print this report" in the upper left corner st the top of the Reports page. It tells use your browser's printing tool, e.g., CTRL-P, File-Pint, for a printout. Tou can also export the information as CSV-tables under the header for "Computed Summaries". If you are not printing to a PDF-file, you probably want to set the printing properties such that it shrinks the page to fit. You also would want to enable printing of background colors if you are interested to see the errors highlighted; offending values are also struck out to identify errors on your printed copy. Both the Reports page and the remaining error and warning messages from the interface feedback strip (if any) are printed. Loops in the scan listing are not automatically collapsed nor expanded; it will print as selected in the scan listing at the time of printing. To print the page with all loops expanded, use the expand-all icon in the header of the Scan List table.

               

              Validation and submission

              When you have created one or more SBs for this PB, go back to the PB page (click on the PB name in the tree of the SBs). In the table at the bottom you will find a summary of your SBs in this PB, with some accounting of the time each SB has consumed. You should check this before you submit your schedule, because your SBs will not be accepted for scheduling if they are using up more time than allocated for your project, or more than allocated for your fixed-date SB.

              If the validation points out that the sunrise/sunset check boxes are ticked, see above how to address this before submitting.

              Once everything is in order, when you are within your time limits and no errors remain, you can submit your SB schedule using the third tab on the SB page (click on the SB name and select the "Validation and Submission" tab page). Subsequently click "Validate" and, if the project passes validation, "Submit". It will send the information to the relevant places within VLA operations and show you a message to that effect. All you need to do now is keep your fingers crossed... Note that you do not send a (observe) file to an NRAO email address as you may have been used to, only press a button. The SB will turn read-only: the SB name will appear in slanted red font.

              When you realize you have an error in your submitted SB, simply select the SB in the tree, and navigate to the "Validation and Submission" tab page. You can cancel your SB submission, which allows you to edit the SB and submit it with your corrections.

              Initially, the status of your submitted SB will appear as "SUBMITTED" on the PB information page (accessible by clicking the name of the PB in the left hand side bar). Your submission will actually put your schedule in a queue that currently is on hold. After we have received your schedule we will check it for technical errors (i.e., for resource settings, elevation requirements, etc.) and release it to the observing queue when it is found to be valid. At this time, its status will change to "SCHEDULABLE", meaning that it is ready for observing.

              4.7. Sharing Catalogs and Projects, and Exiting

              When the project, source and resource catalogs for the project are created by NRAO, all co-I's on the proposal in the PST are able to access and modify the project source and resource lists automatically. This is also the case for project PBs, SBs and scans in the OPT tool. If a co-I decides to delegate scheduling by a co-investigator that was not on the original list of proposers in the PST, use the Properties tab of the catalog and/or the Project page to add individuals known to the NRAO user data base (otherwise they have to register first).

               

              Sharing Catalogs

              However, if you decided to make your (re)sources in a different catalog you have different options to make them available to your collaborators. The most logical way is to start off creating your (extra) (re)sources in the catalogs provided for the project, or to copy the (re)sources from your personal catalog to the project catalog so the catalog name reminds you which project it was used in. If you want to share your newly created catalog with different people, you can again use the Properties tab to add co-I's.

              Another option is to export and import the catalogs through locally saved XML-formatted files. When saved locally you have all freedom to communicate and share with your co-investigators, e.g, that are not in the NRAO data base. You would want to check your catalogs for correctness if you aren't absolutely sure you have already done so before exporting - do not hand-edit the XML files. Exporting unused catalogs and projects, which later can be imported if needed, also keeps the information contained in the OPT web application limited which will speed up the operation over the web. From the top menu strip select FILE - EXPORT or FILE - IMPORT to interact with a dialog window. The default OPT web application file transfer export or import format is XML, but for the SCT the PST format should allow you to read (and write) the same file as you used to submit your source list to the PST. The latter would obviously be very useful for long lists. The upload field or pressing the download button will interact with your local computer environment according to your browser upload and download settings.

               

              Sharing Projects

              As mentioned above, simply add an individual to the project if you like to share it. You can also export your project containing your PBs and SBs to a local disk just like you can save the RCT and SCT catalogs (by selecting FILE - EXPORT) and email the XML files. It may be good practice to do so to keep a copy, and to delete obsolete projects (when not observed) and catalogs when the contents in the OPT web application data base gets large. You will appreciate the increase in speed over the network while you know you can always reload these when you need them again. By the way, the exported XML file is not used for submitting your schedule, just for you and your collaborators to communicate or keep safe.

               

              Exiting

              The proper way to exit the OPT web application is to use FILE - EXIT or click on EXIT on the right-hand side of the blue navigation bar. This will bring you back to the my.nrao.edu portal. Also log out of the portal using the upper right hand side logout link.

              Exiting can also be achieved, or happen, due to a long period of inactivity. As the server-side database updates every time you make a change in the OPT in your local browser, there is no need to worry about unsaved changes if you are timed out.

              Please, do not use the browser back button to navigate to the previous page. This may give you browser errors and might prevent you from working on your project for a few hours.

              5. Subarray Observing

              The 27 VLA antennas can be used in subsets, to observe several independent programs simultaneously. Typical uses are to observe different sources that are bright enough that not all antennas are needed for the full sensitivity, or observing the same source at different observing bands at exactly the same time.

              When preparing for subarray observing, all procedures, advice, and restrictions to create Scheduling Blocks should be followed, as described in the previous sections of the manual. Any source or resource available in the SCT or RCT catalogs, respectively, can be used in creating scans for the subarray. There are no restrictions in sources, resources, scan intervals, scan timing, pointing scans, etc., between the subarrays other than the general limits, including restrictions for General Observing programs (i.e., for semester 18A and 18B up to three independent subarrays using standard 8-bit continuum setups and no special modes such as pulsar, OTF, etc., as that would make it a (Resident) Shared Risk program). There are restrictions in the division of antennas over the subarrays; in particular three subarrays of nine antennas each is not allowed. Further details on using subarrays can be found in the Guide to VLA Observations and the Observational Status Summary (OSS).

               

              Making Subarrays in the OPT

              Currently, creating a subarray schedule in the OPT is implemented by the use of scan loops with different scans (e.g., different sources, or the same sources with differing resources), where the loops are executed at the same time with different subsets of antennas. This is not the optimum implementation and we are working on a better scheme for the future. For the moment please follow these instructions:

              • In the Program Block created for the project and approved for subarray observing, create a Scheduling Block if it is not already present and name the Scheduling Block. The details such as LST start range, weather conditions, count, etc., entered for this Scheduling Block will apply to all the subarray observations.
              • Click on the name of the newly created Scheduling Block in the tree to the left if it is not already active (highlighted). Make sure it is empty, i.e., remove any (default) scan already in the Scheduling Block. Use File-Create New-Subarray to create a new subarray in the Scheduling Block and name the Subarray Loop. Repeat, now or later, for one or two more subarrays (up to three total for General Observing). You must have selected a Subarray Loop (not the Scheduling Block) to create additional ones.
              • Divide the array into subarrays by, per Subarray Loop, ticking the boxes of stations that should make up the subarray configuration. Already used antennas should not be selectable. Note that the numbering is from the center of the array (#1) out to the furthest one on the arm (#9), where N, E, and W stand for the North, East and West arm respectively. The valid principal array configuration (Any, A, B, etc) is specified in the Program Block; the actual antenna pad numbers scale with the principal array configuration but the order specified in the Subarray Loop is in which order the antennas are allocated on each arm per subarray.
              • Create your Scan Lists in each of your subarray. Loops of scans are allowed. Copying scans from one subarray to the next should work as usual, etc. Do not use the tick-box "Keep Previous Conf." for the first scan resource in your subarray. Make sure that the total time per Subarray Loop adds to (almost) the same time, as otherwise the shorter subarrays will be idling while the longest has to finish (and which total time will count toward your allocated time).

              • Once each Subarray Loop contains valid scans, the Reports page of the Scheduling Block can be used to generate resource, source and scan summaries. However, as a WARNING at this time, the Reports summaries include all resources and accumulated time on source over the subarrays. That is, all resources used in any Subarray Loop is listed in a single Resource Summary table. Also, if a source/resource/intent combination appears in more than one Subarray Loop, the total number of scans and total accumulated time is listed in a single Source Summary Table. However, when unfolding the loops in the Scan Listing table, they do list the scan listing per Subarray Loop correcly in the loops, i.e., each loop starts at the same LST to show the scan timings, elevations, etc., of the scans in each subarray. Check the end times of each of the loops to make sure they do not differ too much.
              • Validate the Scheduling Block and submit when done.

               

              Notes

              Subarray observing should be proposed for and be approved by the TAC.

              Subarray observing is General Observing and has restrictions accordingly; e.g., only standard observing with 8-bit continuum resources. Other modes or more than 3 arrays are in the Shared Risk categories.

              A division in three subarrays is typical one of 10, 9 and 8 antennas on the array; a division in two usually has 14 and 13 antennas per subarray allocated. Typical subarray antenna distributions over the whole array are homogeneous, random, or the inner antennas for the higher frequencies in a subarray and the outer for the lower frequency bands in another subarray. The latter is done to attempt to get a similar angular resolution between the observing frequencies.

              Subarrays cannot be generated with text-file uploads of Scheduling Blocks (File-Import Scheduling Block). However, if the Subarray Loop structure is in place, text-file scan lists can be imported in each Subarray Loop separately (File-Import Scans...).

              We are working on creating the three Reports separately for each Subarray Loop in a next update of the OPT, but for now only the Scan Listing summary shows independent information per Subarray Loop.

              6. On-the-fly Mapping and Mosaicking

              On the fly mapping or on the fly mosaicking (OTF, OTFM) scans are different from other scan modes as the data is actually taken while the telescope pointing moves between two points on the sky. This move is done in a linear fashion with a constant slewing speed with respect to the sky. That is, the starting and ending RA and Dec. (J2000) coordinates are taken from the OPT scan, and the telescope slews in the given stripe duration (see below) at a constant speed linearly in RA and linearly in Dec. Thus whereas the scan in east to west and west to east in principle require different absolute telescope slewing rates seen by the operator, the slewing rate on the sky is not affected by the direction of the slew. The scan duration, number of phase center steps and number of visibility dumps per integration determine the interpolation mapping grid and map sensitivity. Note that these OTF slews are using the Mercator projection of the coordinates in RA and Dec and therefore might have map deformation implications for OTF close to the (north) celestial pole.

              For the remainder of this section it is assumed that the observer has consulted the guidelines given in the mosaic page, and that the phase center grid and integration time per pointing are known.

              As OTF modes typically are used to cover a large area of sky in a short time, the default resource integration times may not be sufficiently short. How to set up an OTF resource is described further below.

              OTFM in the OPT

              To observe in OTF mode the OPT needs to know both the beginning and end points of the OTF scan in RA and Dec. (J2000). The scan ranging from the beginning to the end point is referred to as a "strip" or "stripe". Per strip these two boundary target positions should be defined in the source list (SCT) as two separate positions. The intermediate phase centers for the mapping between the beginning and end points are determined by the on-line system as described below. These intermediate points are not displayed in the OPT scan list (reports tab), only the boundary positions. Of course these boundary target points can be entered in the SCT manually, but for any larger (rectangular, hexagonal, etc) grid mosaic, by far the easiest way to do this is to generate the grid in (e.g.) RA for moving in constant Dec. using a text editor and to import this grid with the text import tools given elsewhere. Some examples are given below; end-points other than in equatorial coordinates will be converted to J2000 RA and Dec. internally by the SCT.

              Scan Mode "On The Fly Mosaicking" reveals the required fields to schedule an OTF strip; see the screen shot below. These fields are not only the beginning and ending position of the strip (as defined above), but also some specific settings for defining the strip. The "number of steps" and "integrations per step" require user input. Furthermore, the values for "integration time" and "stripe duration" are derived from the resource selected and the number-of-steps-plus-one times the number-of-integrations-per-step. The "plus-one" is added to the number of steps to account for edge effects (actually an extra iteration at the start that gets flagged in the data). Note that the "stripe duration" is not the same as the "scan timing duration". The latter should include at least 10-15 seconds of overhead to position the telescopes to the beginning of the strip (i.e., to include turn around and settle time) and thus somewhat depends on the angular distance to slew between the observed strips.


              Number of steps (call this variable N):
              The strip is divided linearly in N-1 equal parts between the RA end-points, and similarly in Dec, and thus contains N pairs of (RA,Dec), including the end points. These coordinates will constitute the phase centers used during the strip observation and end up as the "sky target positions" (or mapping grid points) of the data taken along the strip in the visibility data set. Each of these RA,Dec coordinates (fields) can be individually imaged if desired, or selectively included in joint deconvolution algorithms.
              Integrations per step (variable M):
              This is the number of time intervals associated with each phase center, each RA,Dec coordinate above. If individually imaged, the total integration time per field is M*Tvis (see next) and thus a measure for the image sensitivity (but see the mosaicking page for more accurate details).
              Integration time (Tvis):
              This is the integration time per visibility as specified in the resource selected in the resource field.
              Stripe duration (Tstrip):
              The time it will take to complete this strip observation. That is including the startup integration for the strip (i.e., N+1 steps), but excluding the overall startup of slewing the telescopes to the beginning of the strip (i.e., the slew to the strip starting position). This number is calculated as Tstrip = (N+1)*M*Tvis .
              Scan timing (Tscan):
              The total time of the scan, which is the Stripe Duration plus the slewing overhead. The latter needs about 10-15 seconds extra overhead if it is the continuation of a previous strip pattern, e.g. a reversal of the motion at the next strip in the same area of the sky, but otherwise perhaps may need many extra minutes of slew if it is the first strip of a new mosaic. It is possible to absorb the starting slew in a normal scan on the beginning position for the appropriate duration and give it an intent that is easily recognizable for flagging but that would add to overhead. This number thus should be at least Tscan > Tstrip + 10sec. See the scan import example below.
              RA direction:
              Moving between two positions on the sky can be done in several ways: the shortest way, and something else. The default is to choose the shortest direction in RA (and always the shortest direction in Dec). However, the scan moving direction in RA can be explicitly selected using the radio buttons here. Of course, when going the long way instead of the short route, the on-the-sky slew rate calculation below should use the strip angle of the longer path.

              The on-the-sky slew rate is determined by the strip angle (in arcmin or arcsec) and the stripe duration (in minutes or seconds), where the maximum tested slew rate in S-band currently is of the order of 10'/s (10 arcmin per second, which is the same as 10 degrees per minute): slew rate = (Change in angle)/(N*M*Tvis) .

              As for standard scan modes, the data rate is determined by the resource details. That is, as determined by the amount of correlator capacity used and the dump time (Tvis). The resource summary in the RCT will show this number when creating the resource, and the reports summary page top table will also summarize it. Note that for the typically short integration times used in OTF, the data rate quickly will approach or exceed the limits set for General Observing Capability modes.

              Creating an OTF resource

              The main difference between a normal observing scan resource and an OTF resource is that typically the visibility dumps should occur at a rate higher than the potential smearing effects on the data. It is thus advisable to dump at least a few times while the telescopes move a primary beam on the sky, say Tvis(sec) <~ 0.1 x freq(GHz) / slew-rate(arcmin/sec), but this is dependent on the required sensitivity and science goal.

              The resource can be created as described in the OPT RCT section, with the visibility integration time entered in the first tab. However, care should be taken not to exceed the current data rates (shown in the box in the RCT), which happens easily with demanding correlator setups as well as with shorter integration times.

              Current constraints:

              • Phase centers (N) cannot be changed faster than at 0.5 second intervals.
              • Visibility integration (dump, Tvis) times must be at least 250 ms (which would be the integration time in the RCT).
              • Resource data rates may not exceed the limits for (Resident) Shared Risk (25 MB/s, 60 MB/s).
              • Limited slew rates in Azimuth (40 deg/min) and Elevation (20 deg/min) will pose a limit on the maximum slew rate in RA and Dec, depending on geometry (and LST) of the observation. It is best to stay on the safe side of these limits.


              Other notes:

              • Slewing at high elevations should be minimized due to potential tracking and dish deformation issues close to zenith. That is, for OTF targets close to 34 deg Dec., map it well before or after transit, i.e. close to rise or set!
              • Times for dumps are in UTC (which is very close to LST for Tvis << 1 min), scan times are in LST.
              • Individual antennas may start and stop scanning a strip up to 0.5 seconds late with respect to the rest of the array. This will introduce a pointing offset of up to 0.5(sec) x slew-rate for that antenna. To limit imaging problems without flagging that antenna as bad (where it may not be known which antenna it actually is), one would want to keep that offset smaller than about a quarter of the primary beam calculated at the highest frequency in use when planning for potential slew-rates.
              • See mosaicking page for Tvis and other mosaicking hints.


              Examples

              Suppose we observe in X band and follow the mosaicking web page to get the sampling distances, i.e., we assume an observing frequency of 9.33 GHz and hexagonal packing at sqrt(3) which is almost the same as using the upper part of the band and sqrt(2). The primary beam is thus 4.5 arcmin (270 arcsec) and we use a strip separation of 2.6 arcmin (156 arcsec). Remember that (ΔRA in angle) is (ΔRA in time) times 15 × cos(Dec), e.g. 4m at 60d = 4m x 15'/m x cos(60d) = 30 arcmin.

              The minimalistic SCT input files then may look like this (see text-file input):

              1a) A 20-arcmin length, 4-row (10' wide) rectangular area scanned in RA (constant Dec) centered on (J2000) RA=12:00:00, Dec=00:00:00

              row01east ; ; ; ; 11:59:20; +00:03:54; ; ; ; ;
              row01west; ; ; ; 12:00:40; +00:03:54; ; ; ; ;
              row02east ; ; ; ; 11:59:20; +00:01:18; ; ; ; ;
              row02west; ; ; ; 12:00:40; +00:01:18; ; ; ; ;
              row03east ; ; ; ; 11:59:20; -00:01:18; ; ; ; ;
              row03west; ; ; ; 12:00:40; -00:01:18; ; ; ; ;
              row04east ; ; ; ; 11:59:20; -00:03:54; ; ; ; ;
              row04west; ; ; ; 12:00:40; -00:03:54; ; ; ; ;


              1b) A 20-arcmin length, 4-row (10' wide) rectangular area scanned in RA (constant Dec) centered on (J2000) RA=12:00:00, Dec=+60:00:00

              row01east ; ; ; ; 11:58:40; +60:03:54; ; ; ; ;
              row01west; ; ; ; 12:01:20; +60:03:54; ; ; ; ;
              row02east ; ; ; ; 11:58:40; +60:01:18; ; ; ; ;
              row02west; ; ; ; 12:01:20; +60:01:18; ; ; ; ;
              row03east ; ; ; ; 11:58:40; +59:58:42; ; ; ; ;
              row03west; ; ; ; 12:01:20; +59:58:42; ; ; ; ;
              row04east ; ; ; ; 11:58:40; +59:56:06; ; ; ; ;
              row04west; ; ; ; 12:01:20; +59:56:06; ; ; ; ;


              2) A 7-point (3-row, ~8' diameter) hexagonal scanned in RA (constant Dec) centered on (J2000) RA=12:00:00, Dec=00:00:00

              row01east ; ; ; ; 11:59:49.6; +00:02:36; ; ; ; ;
              row01west; ; ; ; 12:00:10.4; +00:02:36; ; ; ; ;
              row02east ; ; ; ; 11:59:39.2; +00:00:00; ; ; ; ;
              row02west; ; ; ; 12:00:20.8; +00:00:00; ; ; ; ;
              row03east ; ; ; ; 11:59:49.6; -00:02:36; ; ; ; ;
              row03west; ; ; ; 12:00:10.4; -00:02:36; ; ; ; ;


              3) A 14-point (5-row, ~13' diameter) hexagonal scanned in RA (constant Dec) centered on (J2000) RA=12:00:00, Dec=+60:00:00

              row01east ; ; ; ; 11:59:39.2; +60:05:12; ; ; ; ;
              row01west; ; ; ; 12:00:20.8; +60:05:12; ; ; ; ;
              row02east ; ; ; ; 11:59:18.4; +60:02:36; ; ; ; ;
              row02west; ; ; ; 12:00:41.6; +60:02:36; ; ; ; ;
              row03east ; ; ; ; 11:58:57.6; +60:00:00; ; ; ; ;
              row03west; ; ; ; 12:01:02.4; +60:00:00; ; ; ; ;
              row04east ; ; ; ; 11:59:18.4; +59:57:24; ; ; ; ;
              row04west; ; ; ; 12:00:41.6; +59:57:24; ; ; ; ;
              row05east ; ; ; ; 11:59:39.2; +59:54:48; ; ; ; ;
              row05west; ; ; ; 12:00:20.8; +59:54:48; ; ; ; ;


              Example Scheduling Block

              An example of a scheduling block that can be created with a text editor and imported in the OPT may look like this (see explanation of the fields):

              # example SB for OTF on W51
              #
              VERSION; 3;
              #
              # rectangular OTF in S band, 8 strips, 0.5s
              #
              # define catalogs in which Sources and Resources can be found by name
              SRC-CAT; OTF, VLA;
              HDWR-CAT; OTF, NRAO Defaults;
              # Scheduling Block details
              SCHED-BLOCK; OTF_W51_S; Dynamic; 1; 2014-06-07; 16:00:00-21:00:00, ; 25.0; D; 225.0; 35.0; N; N; w=100.0,p=60.0; ;
              #
              # startup scans on calibrators
              STD; Dummy; 3C286_S; S16f_otf_0.5; DUR; 1m; cw; N; N; N; N; SetAtnGain,; ;
              STD;3C286;3C286_S; S16f_otf_0.5; DUR; 9m; cw; N; N; N; N; CalFlux, CalGain, CalBP; ;
              #
              # Slew to calibrator close to mapping area
              # slew from calibrator to beginning point of mapping row 1
              # first 4 rows of map
              STD;J1925_S; J1925_S; S16f_otf_0.5; DUR; 6m; ; N; N; N; N; CalGain,; ;
              STD;Setup01; row01left; S16f_otf_0.5; DUR;35s; ; N; N; N; N; ObsTgt,; ;
              OTFM; row01; row01left; row01rght; S16f_otf_0.5; DUR; 144s; 32; 8; 0; ; N; N; N; N; ;
              OTFM; row02; row02rght; row02left; S16f_otf_0.5; DUR; 144s; 32; 8; 0; ; N; N; N; N; ;
              OTFM; row03; row03left; row03rght; S16f_otf_0.5; DUR; 144s; 32; 8; 0; ; N; N; N; N; ;
              OTFM; row04; row04rght; row04left; S16f_otf_0.5; DUR; 144s; 32; 8; 0; ; N; N; N; N; ;
              #
              # Slew to calibrator
              # slew from calibrator to beginning point of mapping row 5
              # next 4 rows of map
              # final calibrator scan
              STD;J1925_S; J1925_S; S16f_otf_0.5; DUR;95s; ; N; N; N; N; CalGain,; ;
              STD;Setup05; row05left; S16f_otf_0.5; DUR;35s; ; N; N; N; N; ObsTgt,; ;
              OTFM; row05; row05left; row05rght; S16f_otf_0.5; DUR; 144s; 32; 8; 0; ; N; N; N; N; ;
              OTFM; row06; row06rght; row06left; S16f_otf_0.5; DUR; 144s; 32; 8; 0; ; N; N; N; N; ;
              OTFM; row07; row07left; row07rght; S16f_otf_0.5; DUR; 144s; 32; 8; 0; ; N; N; N; N; ;
              OTFM; row08; row08rght; row08left; S16f_otf_0.5; DUR; 144s; 32; 8; 0; ; N; N; N; N; ;
              STD;J1925_S; J1925_S; S16f_otf_0.5; DUR;95s; ; N; N; N; N; CalGain,; ;
              #---END---

              7. Text Files and Catalogs in the OPT

              7.1. Text Files

              Apart from direct manual editing in the fields exposed by the web interface, all components of the OPT web application can import and export ASCII text files that, e.g., can be created and manipulated or optimized by computer programs or scripts outside the OPT web application.

              A source list can be prepared from external source catalogs and formatted such that the SCT can ingest it, or a source list can be exported to a text file. Similar catalog operations can be performed on resource catalogs as well.  Furthermore, (re)source lists can be extracted from an existing scheduling block and can be shared or loaded in either the RCT or the SCT.  The OPT can read and write scan lists or ingest script-generated scheduling blocks, etc.

              This section describes the syntax that might be of interest to most users of this feature: importing source lists into the SCT and importing scan lists or complete scheduling blocks into the OPT. A properly formatted standardized list of spectral lines is also provided for upload. To be able to read in scans or scheduling blocks into the OPT without overloading the individual entries with too many variables, the source and resource catalogs must be defined beforehand (so that the scan parser can grab the (re)source definitions from the existing catalogs). If only VLA calibrators and NRAO default resources are required, no other additional (re)source catalogs need to be defined.

              The following sections in this chapter of the OPT manual describe the syntax for importing source lists into the SCT, and for importing scan lists and scheduling blocks into the OPT. For information about importing source lists into the Proposal Submission Tool (PST), see the Sources Section of the PST manual.

               

              General Syntax

              The import of text files is accomplished by parsing each line, where each line is assumed to define a complete instruction. Parsing occurs for plain ASCII characters so if a rich-text capable text editor is used (e.g., Word) please save without rich-text formatting in plain ASCII text or the import will fail without an error message. Empty or whitespace-only lines and lines where the first non-whitespace character is a hash (# symbol) are ignored. That is, hashes may be used to insert comments in the text file. Typical lines will have input fields delimited by semi-colons (;), where multi-variable fields have their variables separated by commas (,). The comma after the final value of a field is optional, but the final semi-colon after the final field is mandatory (except for spectral line lists). Leading and trailing whitespace around field variables is ignored, but whitespace between the first and last non-whitespace character of a variable is preserved (see examples). Optional fields may be left unspecified (i.e., no characters or whitespace-only characters) and will be assigned a default value where appropriate. Character fields are treated as case-sensitive unless otherwise specified. Illegal characters in (free-format text) fields are non-printable (tab) characters, including any form of end-of-line characters, variable delimiters (semi-colon and comma) and any of the specified ones in the table below; leading and trailing whitespace around free-format text variables is ignored, but whitespace within freeformat text is preserved. The full list of acceptable and illegal characters in free-format text fields is:

              Acceptable characters
              a-zA-Z lower and upper case letters
              0-9 digits
              space
              + - . = plus, minus, period/decimal and equal signs
              / _ # * slash, underscore, hash/sharp and "star"
              ( ) [ ] open/close parentheses and square braces
              Illegal characters
              ' " single quote and double quote
              { } curly braces
              < > less than and greater than

              end-of-line and non-printable characters (e.g. "tab"),

              rich-text formatted text or other non-ASCII characters

              \ @ % $ backslash, at, percent and dollar signs
              ` ~ ! ^ & | : , ; other textual and linguistic characters

              7.2. Source Lists

              Syntax

              Text files with source lists can be imported into the SCT (and PST) if they use the following syntax. Every line containing any source information in the file must define a separate source as:

              sourceName;groupNames;coordSystem;epoch;longitude;latitude;refFrame;convention;velocity;calibrator;
              

              The text file should only contain lines formatted as above, or lines that are known to be ignored by the parser (i.e., empty or whitespace-only lines and comment lines starting with a #-hash). An (optional) exception is if the very first line is starting with a *-star; the string after the star will replace the default source catalog name. Start with the catalog name syntax line before any source syntax line or any comment line or this source catalog name will not be picked up (and an "Unnamed Catalog" results):

              * Source catalog name in the SCT
              # this is a line with a comment and the previous line is the syntax used to include all sources into a non-default
              # (the catalog name line will be ignored by the PST when uploading this file)
              # the rest of the source list file contains source lines mandated as above and other ignored lines
              <source1 line>
              <source2 line>
              ...

              Every data line must have ten semi-colons (;) , including the one after the final calibrator field. Details and possible (predefined) values per field are described here:

              sourceName Mandatory, single value
              Unique name for the source, free-format text. Multiple lines with the same source name, longitude, latitude and velocity information (below) will end up as a single source entry
              groupNames Optional, unlimited number of comma-separated values
              Group(s) or sub-catalog(s) to which this source belongs, free-format text. If no group name is given the source will be listed in the main (top-level) catalog only
              coordSystem Optional, single value (defaults to equatorial), not case-sensitive
              Coordinate system in which longitude and latitude angles below are defined, typically Equatorial for source coordinates in RA and Dec. (the default). Valid options are: Ecliptic, Equatorial, Galactic. Sources converted to other, e.g., equatorial coordinates will show an asterisk with the converted coordinates in the catalog
              epoch Optional, single value (defaults to J2000), not case-sensitive
              Epoch for which longitude and latitude angles below are defined, valid options are: B1950, J2000
              longitude Mandatory, single value
              An East-West angle, typically Right Ascension. Valid options are a numerical value in decimal degrees or a sexagesimal colon-delimited value in hh:mm:ss.sss. . . (with or without leading zeros) for hours : minute : seconds. Either form may be preceded by the plus (+) or minus (−) sign
              latitude Mandatory, single value
              A North-South angle, typically Declination. Valid options are a numerical value in decimal degrees or a sexagesimal colon-delimited value in dd:mm:ss.ss. . . (with or without leading zeros) for degrees : arcminute : arc-seconds. Either form may be preceded by the plus (+) or minus (−) sign
              refFrame Mandatory in combination with convention and velocity, single value, not case-sensitive
              The reference frame in which the velocity below should be interpreted. If any of refFrame, convention or velocity is specified, all three must be specified to make sense. Leave all three blank if no velocity information should be included in the source properties. Useful valid options with their abbreviations are: Barycentric (Bary), LSR Kinematic (LSR or LSRK), Topocentric (Topo)
              convention Mandatory in combination with refFrame and velocity, single value, not case-sensitive
              The frame definition in which the velocity below should be interpreted. Useful valid options are: Optical, Radio, Redshift
              velocity Mandatory in combination with refFrame and convention, single value
              A decimal number, optionally preceded by the plus (+) or minus (−) sign, to express the source velocity in km/s, or to express the source redshift in z if the convention above is Redshift
              calibrator Optional single value (defaults to N), not case-sensitive
              A value of Y or N to indicate whether a source is to be used as calibrator. The SCT will ignore this field; it is retained to maintain compability with the PST and other tools. Instead, calibrators for the VLA are identified with scan intents in the OPT.

               

              To ingest a text file with a source list, navigate to the SCT. Select from the menu FILE - IMPORT and then PST for the import format. After providing a file to import, a new catalog with the default name “[Unnamed Catalog]” will be created. If the imported sources need to be included in a different catalog, or a different catalog group, use the general copy/paste method of the OPT web application to move the sources around. Alternatively, change the name of the new unnamed catalog in the SCT using the "Properties" tab of that catalog if a name was not specified with a *-star line.

              Source List Examples (in SCT/PST format)

              Minimalist. Source name and coordinates only, default coordinate system, epoch and unspecified velocity:

              J0433+0521;;;;04:33:11.095535;05:21:15.619420;;;;;
              J1119−0302;;;;11:19:25.3;−03:02:51.32;;;;;
              <some_name> <4 times ";"> <RA_j2000> ; <Dec_j2000> <5 times ";">


              Explicit. Same data as minimalist, above, but with coordinate system and epoch stated in long form, and spaces for ease of reading:

              J0433+0521; ; equatorial; J2000; 04:33:11.095535;  05:21:15.619420; ; ; ; ;
              J1119−0302; ; equatorial; J2000; 11:19:25.3 ; −03:02:51.32 ; ; ; ; ;


              Full. All fields are specified, starting by naming the catalog "MyPrivateList" in which these sources should appear (instead of the default "Unnamed Catalog"); multiple values in those fields that allow it, with spaces in source and group name, some case-preserved and case-ignored variable names, and with optional trailing comma in velocities.

              * MyPrivateList
              # This is my private list of secret sources..
              Secret Source; My Recipes, Private; equatorial; J2000; 12:34:56.789; 87.65432; lsR; Optical; −98.6,; y;

              7.3. Importing Scheduling Blocks

              Scheduling Blocks and Scan Lists

              First, note the differences between importing scan lists and importing complete scheduling blocks:

              • A text file representing a complete scheduling block (SB) defines not only the scan list, but also defines the variables needed for a scheduling block
              • Importing scheduling blocks will create a new SB entry in the active Program Block, whereas importing a scan list will add the scans to an active Scheduling Block directly after the active scan, or at the start if the active field is the SB name.

              In this section we discuss the scheduling block preamble, and in the next we describe importing scan lists. Note that we are creating experimental scripts that take an ordered list of source names and produce a text file for import into the OPT. This should be helpful to create simple observing schedules. Please let the NRAO Helpdesk know if you are interested in trying this out.

               

              Scheduling Block Preamble

              A text file defining a scheduling block has to begin with the following case-sensitive content (boldface lines are mandatory):

              VERSION;versionNumber;
              SCHED-BLOCK;schedBlockName;schedulingType;iterationCount;date;timeOfDay;shadowLimit;. . .
              . . .shadowCalcConfiguration;initTeleAz;initTeleEl;avoidSunrise?;avoidSunset?;. . .
              . . .windApi;commentsToOperator;


              The VERSION line is optional, but if present it must be the first data line and include an integer versionNumber in the second field between two semi-colons (;). The current maximum versionNumber is 3. If the line is omitted, versionNumber defaults to the latest version of the syntax.

              The SCHED-BLOCK line distinguishes a complete scheduling block input text file from a scan list input text file.  Only a single SCHED-BLOCK line is allowed in the file and has to precede any scan list lines (below). If it is not present the file will be interpreted as a scan list only file as described later. Apart from the data field identifier “SCHED-BLOCK”, this line includes 13 fields and exactly 14 semi-colons (;), including the last. Details and possible (predefined) values per field are described in the table below. Note that unless specified otherwise, the parsing of strings is case sensitive:

              schedBlockName Optional, single value (defaults to [New Scheduling Block])
              Name to give to the scheduling block, free-format text
              schedulingType Optional, single value (defaults to Dynamic), not case-sensitive
              Scheduling type, valid options are: Dynamic, Fixed
              iterationCount Optional, single value (defaults to 1)
              Integer, maximum number of times to observe the scheduling block (Dynamic scheduling type only)
              date Mandatory single value for Fixed, optional multi-value for Dynamic scheduling type
              Fixed: an observing date, either in "yyyy-mm-dd" format for UTC or a five-digit integer that is interpreted as the VLA LST day (e.g., 2012-07-25 or 62859). The parser will bail out of creating the scheduling block if this date is not in the future
              Dynamic: if provided, the earliest and latest UTC date and time that this scheduling block may be run; must be formatted as "yyyy-mm-dd hh:mm:ss, yyyy-mm-dd hh:mm:ss" where the ending date and hh:mm:ss parts are optional. If nothing is provided it defaults to the date that the OPT scheduling block is created for the early start, and a date far in the future for the latest start
              timeOfDay Mandatory single value for Fixed, optional multi-value for Dynamic scheduling type
              Fixed: time of day in hh:mm:ss format at which the schedule must start. If the date is in yyyy-mm-dd format the time is interpreted as UTC but if the date is a five-digit integer (i.e., without thousand-separators) it will be interpreted as LST.
              Dynamic: a comma-separated list of LST start ranges where each range takes the form “hh:mm - hh:mm” where all whitespace is ignored. It defaults to “00:00-24:00” which is only sensible for a scheduling block with only circumpolar sources (Declination > 64 degrees). This implies that any dynamic scheduling block with a standard VLA flux calibrator needs a non-default LST start range
              shadowLimit Optional, single value (defaults to 0.0)
              Numerical value in meters (0 to 25) for issuing shadowing warnings in the scheduling block report when an antenna is shadowed by another by this value or more
              shadowCalcConfiguration Optional, single value (defaults to the first array configuration in the Program Block)
              The array configuration for which the above shadowing calculation is performed. Valid values: A, B, C, D and Any (case-sensitive!). "Any" implies calculations for the worst case, i.e., "D". When provided, the array configuration has to match one of the array configurations in the program block or it will revert to the default value. The hybrid configurations (e.g., BnA) are also allowed but not in use anymore
              initTeleAz Optional, single value (defaults to 225)
              Assumed antenna pointing direction in degrees Azimuth at the start of the observation, used to calculate slewing time to the first source. Valid range: −85.0 to +445.0, where an Azimuth of 180° points toward the south
              initTeleEl Optional, single value (defaults to 35)
              Assumed antenna pointing direction in degrees Elevation at the start of the observation, used to calculate slewing time to the first source. Valid range: +8.0 to +90.0, where an Elevation of 90° points toward the Zenith and where the lower Elevation limit is 8.0°
              avoidSunrise? Optional, single value (defaults to N), not case-sensitive; leave blank for Fixed
              Should this scheduling block avoid observing at sunrise, i.e., should this scheduling block not overlap in time between 10 minutes before and 60 minutes after the actual sunrise time? Valid values: Y, N. This field must be left blank for Fixed time scheduling blocks
              avoidSunset? Optional, single value (defaults to N), not case-sensitive; leave blank for Fixed
              Should this scheduling block avoid observing at sunset, i.e., should this scheduling block not overlap in time between 10 minutes before and 60 minutes after the actual sunset time? Valid values: Y, N. This field must be left blank for Fixed time scheduling blocks
              windApi Mandatory for Dynamic scheduling type, single or dual value; leave blank for Fixed
              The maximum allowable wind speed and atmospheric phase fluctuations that are allowed to start observing this scheduling block. Valid entries are either the (case-sensitive!) character designations per observing band (Q, Ka, K, Ku, X, C, S, L or Any - for sub-GHz use Any), which provide pre-defined wind and API limits, or a direct numerical entry for both wind speed (in m/s) and API rms phase (in degrees) as a dual-valued entry.  The format for the latter is “w=#,p=#” (w and p in lower case) with # an appropriate non-negative numerical value (wind < 18 m/s, rms phase < 180 deg). Whitespace and reverse order are allowed as long as both variables with values are explicitly specified. This field must be left blank for Fixed time scheduling blocks
              commentsToOperator Optional, single value
              Comments to the operator, free-format text

               

              To ingest a text file with a scheduling block, navigate to the OPT and activate (click) the program block or a scheduling block in the program block in which the new scheduling block should be placed. Select from the menu FILE - IMPORT SCHEDULING BLOCK. After providing a file name to import, a new scheduling block with the default name “[New Scheduling Block]” will be created if no predefined name is given in the first field of the SCHED-BLOCK line. Note that if FILE - IMPORT SCHEDULING BLOCK is grayed out, the wrong item in the project tree is selected (e.g., a scan).

              Scheduling Block preamble Examples

              Version line and fixed date observing specified in VLA LST day and time:

              VERSION; 3;
              SCHED-BLOCK; Orion Neb; Fixed; ; 72987; 13:45:30; ; ; ; ; ; ; ; Coord w/ HST;

              Dynamic observing, with repeat, multiple LST start ranges, shadow calculations and weather settings for X band, and avoid sunset and sunrise with a comment to run with 20 antennas or more.

              SCHED-BLOCK;Orion;Dynamic;3;2012-08-11;09:30-13:00,18:00-00:30;0;;180;45;y;y;X;>=20 antennas;

              Absolute minimum specifies mandatory wind and API for Dynamic blocks with the receiver letter code only (but then one would be wise to edit the scheduling block name, etc., directly in the OPT).

              SCHED-BLOCK;;;;;;;;;;;;Ka;;

              Absolute minimum for a Fixed scheduling block includes a fixed starting time (here in LST) at the VLA.

              SCHED-BLOCK; ; Fixed ; ; 72859 ; 08:45 ;;;;;;;;;

              7.4. Importing Scan Lists

              Scan lists

              To define a scan list, the standard case-sensitive(!) text file content must start with (boldface lines are mandatory):

              SRC-CAT;sourceCatalogNames;
              HDWR-CAT;hardwareCatalogNames;

              These catalog lines must be included before any scan line described below, and currently also before the SCHEDBLOCK line described from the previous section.  The following table contains a more extensive description:

              type of linefielddescription
              SRC-CAT sourceCatalogNames Mandatory, multi-value
              Comma-separated list of names of source catalogs in order of priority, highest priority first. Source names below must be pre-defined with source properties in at least one of the included catalogs, where the first match will be the one that defines the source in this scan. In practice, one would list the personal source catalogs containing sources for this scheduling block and end with the standard “VLA” calibrator catalog if the calibrators to be used were not copied to the personal catalog
              HDWR-CAT hardwareCatalogNames Mandatory, multi-value
              Comma-separated list of names of resource catalogs in order of priority, highest priority first. Resource names below must be pre-defined with resource properties in at least one of the included catalogs, where the first match will be the one that defines the resource in this scan. In practice, one would list the personal resource catalogs containing resources for this scheduling block and end with the standard “NRAO Defaults” (note the upper-case D in Defaults) catalog for continuum and pointing setups

               

              Text files with scan lists can be imported into the OPT if they use the following syntax. Every line containing any scan information in the file must define a separate scan as one of the following options:


              STD;scanName;sourceName;resourceName;timeType;time;antennaWrap;applyRefPtg?;applyPhase?;. . .
              . . .recordOnMark5?;allowOverTop?;scanIntents;comments;

              PTG;scanName;sourceName;resourceName;timeType;time;antennaWrap;applyRefPtg?;applyPhase?;. . .
              . . .recordOnMark5?;allowOverTop?;comments;
              TIP;scanName;azimuth;resourceName;tippingOrder;comments;
              OTFM;scanName;sourceName(beg);sourceName(end);resourceName;timeType;time;numSteps;numIntPs;. . .
              . . .RAdirection;antennaWrap;applyRefPtg?;applyPhase?;recordOnMark5?;allowOverTop?;comments;

              Standard, Pointing, and On-the-fly Mosaicking mode scans

              Standard observing mode, or STD-scans, require 12 additional fields (in the numbered order below) and 13 semicolons (;), including the last. Pointing mode scans, or PTG-scans, necessary only for observations at the higher frequencies (Ku, K, Ka, Q), have 11 additional fields and 12 semi-colons (;), including the last. Similarly, Tipping mode scans, or TIP-scans, are described with 5 additional fields and 6 semi-colons (;), including the last. On-the-fly Mosaicking (OTFM) scans are defined with 15 additional fields and 16 semi-colons. The following table contains a more extensive description of the fields for STD, PTG or OTFM lines::

              order field description
              STD PTG OTFM
              1 1 1 scanName Optional, single value (defaults to the source name (below) or [New Scan])
              The name to be given to the scan
              2 2 2, 3 sourceName Mandatory, single value
              A source name with its properties (such as sky coordinates) must pre-exist in one of the source catalogs included in the list in sourceCatalogNames in the SRC-CAT line. If you use an alias (B1950, NGC, 3C, Messier name, etc.) as source name instead of the standard 10-digit J2000 calibrator or target name in your scheduling block, please make sure to include this source name with the J2000 coordinates in one of your listed source catalogs. Note that for OTFM-scans, both a beginning and end source position name must be entered in two different columns. Also be alerted that calibrators in the VLA catalog use capital letters (J#, and 3C# for the standard flux density calibrators) in their designation
              3 3 4 resourceName Mandatory, single value
              A resource name with its properties (such as receiver observing band, etc.) must pre-exist in one of the resource catalogs included in the list in hardwareCatalogNames in the HDWR-CAT line. The special term prev (not case-sensitive) can be used to indicate that there is no resource change from the previous scan, though this term is not allowed in loops
              4 4 5 timeType Optional, single value (defaults to Duration LST), not case-sensitive
              The timing method used for the scan. Valid options with their 3-letter abbreviations are: Duration (LST) or DUR, On-Source (LST) or SRC, Stop Time (LST) or END, Duration (UT) or UTD, On-Source (UT) or UTS, Stop Time (UT) or UTE
              5 5 6 time Mandatory, single value
              Time measure for the scan, typically a scan length in the form of hh:mm:ss.s or αhβmγs, but for stop times an absolute hh:mm:ss.s time of (LST or UT) day. Note that 01:02 is interpreted as 1h 2m, and that 01:2.0 is interpreted as 1m 2.0s so it is safest to use the full h:m:s format with two colons (:) or explicitly write it as 1m 2.0s (with or without spaces) if that is what is meant
              - - 7 numSteps Mandatory, single value
              The number of steps, number of phase centers along a strip or stripe. See the OTFM mode description on the special modes page (OPT, section 5)
              - - 8 numIntPs Mandatory, single value
              The number of integrations per step, per phase center. See the OTFM mode description on the special modes page (OPT, section 5)
              9 RAdirection Mandatory, single character
              For any two points in the sky there is a shortest path between them in RA as well as a path to go the other way and take the long slew in RA (there is only one way allowed in Dec, the shortest way). Using the character '0' (zero) will select the shortest path between the starting point (2nd parameter) and the end point (3rd parameter). To explicitly fix the motion in RA, use a plus or a minus sign to observe in increasing RA direction ('+') or in decreasing RA direction ('-'), respectively. Valid values: +, -, 0 (zero)
              6 6 10 antennaWrap Optional, single value (defaults to No Preference), not case-sensitive
              Specified antenna azimuth wrap for the scan. Valid values: R, CW, Clockwise, No Preference, L, CCW, Counterclockwise
              7 7 11 applyRefPtg? Mandatory, single value, not case-sensitive
              Should this scan use previously determined reference (antenna) pointing offsets? Needs a preceding PTGscan to be effective. Valid values: Y, N
              8 8 12 applyPhase? Optional and only for phased VLA observations, single value (defaults to N), not case-sensitive
              Should this scan use previously determined delay and phase (autophasing) solutions? Needs a preceding STD-scan with DetAutoPh intent (see below) to be effective, and usually not used. Valid values: Y, N
              9 9 13 recordOnMark5? Optional and only for phased VLA VLBI observations, single value (defaults to N), not case-sensitive
              Does this scan need recording for correlation with other antennas? Do not use unless you know what this means and you really need it. Valid values: Y, N
              10 10 14 allowOverTop? Optional, single value (defaults to N), not case-sensitive
              Allow the antennas to tip to the other side of the zenith, to Az+180? Do not use unless you know what this means and you really need it. Valid values: Y, N
              11 - - scanIntents (STD-scan only) Mandatory, multi-value, not case-sensitive

              All intents for each scan should be listed. The full list of intents, including all intents for operations, is collected in the documentation mentioned above. The most useful valid options for normal observing, with their full meaning in parentheses are:
              ObsTgt (observe the target, usually not combined with any other intent),
              CalGain (calibrate phase and amplitude gains together, in particular for standard calibration loops on the target source),
              CalFlux (determine the absolute flux density calibration, typical on the handful of standard VLA flux calibrator sources),
              CalBP (bandpass calibration on a strong continuum source),
              SetAtnGain (set various types of antenna gains),
              CalDelay (delay calibration if the bandpass calibration scans are not suitable for delay calibration, or to explicitly name a scan for this purpose),
              CalPolAng (scan on a source with a known polarization angle for calibration of the absolute polarization angle in polarized target sources),
              CalPolLeak (calibration scans to resolve the differences and cross-contamination between the two orthogonally measured polarizations).

              Note that the separate scan definition for a pointing scan or OTF only differs from a standard scan because the scan intent is fixed for those scans; pointing scans may indeed also be phased up and recorded for VLBI correlation

              12 11 15 comments Optional, single value
              Any comments for personal use such as reminders or purpose, free-format text

               

              Note that in principle only a single one of STD/PTG/TIP/OTFM scans in the scan list is required, but it does not make sense to not have any STD-scan in a normal observation scheduling block.

              Tipping mode scans

              Please note that tipping scans currently are not supported. They are being re-implemented as continuous (versus discrete) tipping scans - this section will change in the near future as it reflects the implementation as it was in the past. If you have questions about using TIP-scans please consult the NRAO Helpdesk.

              Tipping mode scans will use a fixed scan length of 5 minutes to be able to derive a useful measurement and therefore have no scan timing field. The following table contains the fields expected on a TIP line:

              orderfielddescription
              1 scanName Optional, single value
              The name to be given to the scan
              2 azimuth Mandatory, single value
              Numerical value in degrees azimuth at which a tipping scan should be performed. Valid range: −85.0° to +445.0°
              3 resourceName Mandatory, single value
              A resource name with its properties (such as receiver observing band, etc.) must pre-exist in one of the resource catalogs included in the list in hardwareCatalogNames in the HDWR-CAT line. The special term prev (not case-sensitive) can be used to indicate that there is no resource change from the previous scan, though this term is not allowed in loops
              4 tippingOrder Mandatory, single value, not case-sensitive
              Elevation movement while performing the tipping scan. Valid values: Up or Low To High, Down or High To Low in elevation (underscores may be omitted). Scan length will be fixed to 5 minutes
              5 comments Optional, single value
              Any comments for personal use such as reminders or purpose, free-format text

              Scan loops

              Loops of scans can be defined (with 4 additional fields and 5 semi-colons) and nested without limitation, and every LOOP-START line must have a corresponding LOOP-END (with no other fields and a single semi-colon). The uppermost unpaired LOOP-END is taken to end the lowermost unpaired LOOP-START.

              LOOP-START;loopName;iterationCount;bracketed?;comments;
              [some STD-scans and/or PTG-scans, TIP-scans, nested loops, etc.]
              LOOP-END;

              The following table describes fields expected on a LOOP-START line:

              orderfielddescription
              1 loopName Optional, single value (defaults to [New Loop])
              Name of the loop, e.g. to remind oneself of the content when collapsed in the scheduling block tree
              2 iterationCount Mandatory, single value
              Integer number, maximum number of times to observe the loop of scans at this point in the schedule
              3 bracketed? Optional, single value (defaults to N), not case-sensitive
              Specifies whether the loop is a “bracketed” loop, i.e., whether the first scan of the loop is repeated at the very end of all loop iterations. Valid values: Y, N
              4 comments Optional, single value
              Any comments for personal use such as reminders or purpose, free-format text

              Importing a scan list

              To ingest a text file with a scan list, navigate to the OPT and activate (click) the scheduling block or a scan in the scheduling block in/after which the new scans should be placed. Any lines relating to the scheduling block preamble will be ignored at this stage. Select from the menu FILE - IMPORT SCANS. After providing a file name to import, scans will be appended directly after the activated field, i.e., at the beginning of a scheduling block if the scheduling block is active, or after the activated scan. The imported scans can be moved around with the the general copy/paste method of the OPT web application.


              Examples

              Following are some very simple examples for 8-bit correlator modes; for 3-bit modes additional setup scans are needed and may be recommended for 8-bit as well. An example of an OTFM scheduling block is given in the OPT manual, OTFM section.

              Example of a scan list with two (8-bit) low-frequency science resources (thus no pointing) starting with target observing and ending with flux calibration scans at the end of the observation:


              # Start with defining which pre-defined source and resource catalogs to use
              SRC-CAT; My Sources, VLA;
              HDWR-CAT; My Resources, NRAO Defaults;
              #
              # Two one-minute 8-bit frequency setup scans, CW wrap, no cal.intents
              STD; setupDummy1; J1404+6551; L full width; dur; 0:01:0.0; CW;n; ; ; ; SetAtnGain,;dummyL ;
              STD; setupDummy2; J1404+6551; my S band; DUR; 0:01:0.0; CW;N; ; ; ; SetAtnGain;dummyS;
              #
              # Account for slew and wrap, may take ten mins minus above, alternate flux calibrator
              LOOP-START; finish 10min startup loop; 2; N; ;
              STD; ; J1404+6551; my S band ; ; 0:2:0; CW; N;;; ; CalGain;;
              STD; ; J1404+6551; L full width; ; 0:2:0; CW; N;;; ; CalGain;;
              LOOP-END;
              #
              # Target observing loop; save on some slewing time
              LOOP-START; target+cal both freqs; 15; N; ;
              LOOP-START;19min scan; 2; ;keep scans under 10min by repeating it;
              STD; ; source1atL; L full width; ; 0:09:30.0;; N;;;; ObsTgt,,; ;
              LOOP-END;
              STD; ; source2atS; my S band; ; 0:07:30.0;; n;;;; ObsTgt,,; ;
              STD; calS; J1404+6551; my S band ; ; 0:2:0; ; n; ;;; CalGain; ;
              STD; calL; J1404+6551; L full width; ; 0:2:0; ; N; ;;; CalGain,;;
              LOOP-END;
              #
              <etc>
              #
              # Slew to the flux calibrator, needs some extra time on first scan, deal with wrap issues
              STD ; L FXBP ; J1331+3030 ; L full width; ; 0:07:20 ; CW; N; ; ; ; CalBP, CalFlux ; ;
              STD ; S FXBP ; J1331+3030 ; my S band ; ; 0:2:0 ; CW; N; ; ; ; CalBP, CalFlux ; ;

              Example of the start of a scan list with two (8-bit) high-frequency science resources, pointing and flux calibration at the start of the observation:


              # Start with defining which pre-defined source and resource catalogs to use
              SRC-CAT; My project sources, VLA;
              HDWR-CAT; HIGHFreqCat, NRAO Defaults;
              #
              # Two one-minute 8-bit frequency setup scans, CCW wrap, no cal.intents
              STD; setup–Q; J0137+3309; Q wide band; dur; 0:01:0.0; CCW;n;; ; ;SetAtnGain,;dum setup;
              STD; setup–A; J0137+3309; special ka band; dur; 0:01:0.0; CCW;N;;; ; SetAtnGain;dum;
              #
              # Account for slew, add time for pointing, may take twelve mins minus above
              PTG; pointing ; J0137+3309 ; Primary X band pointing; ; 0:10:0 ; CCW; N; ; ; ; ;
              #
              # Standard calibration, note the “Y” to apply pointing solutions
              STD ; Q FXBP ; J0137+3309 ; Q wide band; ; 0:1:30 ; ; y; ; ; ; CalBP, CalFlux ; ;
              STD ; A FXBP ; J0137+3309 ; special ka band; ; 0:1:30 ; ; Y; ; ; ; CalBP, CalFlux ; ;
              #
              # Slew to calibrator, need to do a new pointing scan (should have >2:30 on source for all start LST)
              PTG; pointing ; TargPTG ; Primary X band pointing; ; 0:6:20 ; ; N; ; ; ; ;
              #
              # Bracketed loop in first frequency, switch on reference pointing
              LOOP-START; qloop; 17; y; ;
              STD; ; TargCAL ; Q wide band; ; 0:1:0; ; Y;;; ; calgain; ;
              STD; ; myTarget; Q wide band; ; 0:2:30; ; y;;; ; obstgt;;
              LOOP-END;
              #
              # New pointing scan (should have >2:30 on source for all start LST)
              PTG; pointing ; TargPTG ; Primary X band pointing; ; 0:2:50 ; ; N; ; ; ; ;
              #
              # Non-bracketed loop to account for extra time to slew from pointing
              STD; ; TargCAL ;special ka band;;0:1:20;;y;;;;calgain;;
              LOOP-START; Ka-loop; 13; n; ;
              STD;;myTarget;special ka band;;0:2:30;;Y;;;;obstgt;;
              STD;;TargCAL ;special ka band;;0:1:00;;y;;;;calgain;;
              LOOP-END;
              #
              <etc>

              7.5. RCT Spectral Line Lists

              Syntax

              The RCT uses rest frequencies and corresponding spectral line definitions when attempting to set up the WIDAR correlator and populate the subbands in the basebands. Filling out the line parameters takes some effort and has to be repeated for each new resource. Therefore, in the resource lines tab in the RCT, it has a feature to export and import line definitions using plain (editable) text files. Note that the main intended use is to export lines from one resource to import in another, not to create one from scratch (we give no guarantees that it will be parsed properly in that case). Another item to note is that the source position for Doppler setting is not retained in the text file export and thus cannot be defined for text file import. Note that we created a template at the bottom of this page. Every line containing any spectral information in the file must use the following syntax:

              lineName;restFreq;refFrame;convention;velocity;velRange;velSep;polProd;other
              

              The text file should only contain lines formatted as above, or lines that are known to be ignored by the parser (i.e., empty or whitespace-only lines and comment lines starting with a #-hash). Every data line must have eight semi-colons (;), which means that there is none after the final field. Multi-value fields use commas as item separators. Details and possible (predefined) values per field are described here:

              lineName Mandatory, single value
              Name for the setup definition, free-format text, e.g., "SiO v=1"
              restFreq Mandatory, single value larger than zero, unit defaults to GHz
              Rest frequency of the line to place, e.g., "43.122GHz". Note that a unit should not be separated from the value (i.e., no space between them). MHz, kHz and Hz are also accepted
              refFrame Mandatory, single value, not case-sensitive
              The reference frame in which the velocity below should be interpreted. Useful valid options with their abbreviations are: Barycentric (Bary), LSR Kinematic (LSR or LSRK), Topocentric (Topo)
              convention Mandatory, single value, not case-sensitive
              The frame definition in which the velocity should be interpreted. Useful valid options are: Optical, Radio, Redshift
              velocity Mandatory, single value, unit defaults to km/s
              A decimal number, optionally preceded by the plus (+) or minus (−) sign, to express the source velocity in km/s (or m/s), or to express the source redshift in Z if the convention above is Redshift. For Redshift including the unit "Z" is a must, e.g., "0.0443Z"
              velRange Mandatory, single value larger than zero, unit defaults to km/s, value defaults to 100 (i.e., 100.0km/s)
              The minimum velocity range, in km/s (or m/s), that this line should cover when converted to a subband. Essentially this is the subband width, in units of Hz, that is the upper rounded power of two matching this velocity range
              velSep Mandatory, single value larger than zero, unit defaults to km/s, value defaults to 1 (i.e., 1.0km/s)
              The maximum spectral channel separation, in km/s (or m/s), that this line should sample when converted to a subband. Essentially this is the channel width, in units of Hz, that is the lower rounded power of two matching this velocity sampling. Note that a small value may not be possible without requesting recirculation, as the maximum number of channels per subband (of any width) is 256 divided by the number of polarization products (see next)
              polProd Mandatory, multi-value, not case-sensitive
              Number of polarization products recognized as FULL, DUAL or a comma separated list of LL, RR, RL, LR. For linear polarization use either FULL or DUAL
              other Optional, multi-value, not case-sensitive
              This is a grab-all for other pre-defined items that can be specified. Currently it is only used to specify whether the line setup tool should attempt make use of recirculation or not. These options currently are parsed as "USE_RECIRCULATION=true" or "USE_RECIRCULATION=false" respectively. Using recirculation will put a smaller strain on the requirements for baseline board pairs. Note that this is not a comments field for personal notes

              To export a line list from a resource, navigate to the lines tab for the resource in the RCT. At the bottom of the tab, use the "Download Spectral Lines" button. Similarly, use the "Import Spectral Lines" button to attach line definitions to a resource. In the latter case do not forget to specify the source position used for Doppler setting.

              Spectral Line List Example

              This is a single line list as exported from the RCT. A text editor can be used to add lines using the same syntax to be loaded back in to a (new) resource. Note that there is no space between values and units, and that there is no hook to specify the Doppler position.

              # Line name ; Rest frequency ; Rest frame ; Velocity convention ; Velocity ; Minimum range ; Channel separation ; Polarization products ; Additional specifications
              Google X; 14.99GHz; Barycentric; Optical; 87801.0km/s; 303.0km/s; 0.07km/s; DUAL; USE_RECIRCULATION=true

              As a service, we have compiled a list of important lines (according to the IAU), supplemented with lines commonly observed with the VLA below. Copy/paste the lines of your interest (or the whole list) in a text editor to modify according to your specific requirements. Then upload the modified lines, after creating a new 8-bit or 3-bit resource in the RCT, using the resource Lines tab and "Import Spectral Lines" at the bottom of that tab.

              IAU line frequency list formatted for the VLA OPT/RCT

              #The IAU list of important spectral lines (www.craf.eu/iaulist.htm) below 120 GHz, supplemented by selected
              #lines from the Lovas catalog (physics.nist.gov/cgi-bin/micro/table5/start.pl) below 50 GHz.
              #Other lines can be obtained from the web pages above or e.g. the Splatalogue (www.cv.nrao.edu/php/splat/)
              #
              # Line name ; Rest frequency ; Rest frame ; Velocity convention ; Velocity ; Minimum range ; Channel separation ; Polarization products ; Additional specifications
              #
              #  --  P band  --
              D;       327.384MHz; Topo; Redshift; 0.01Z; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              #  --  L band  --
              H;      1420.406MHz; Topo; Redshift; 0.01Z; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              OH;     1612.2310MHz; LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              OH;     1665.4018MHz; LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              OH;     1667.3590MHz; LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              OH;     1720.5300MHz; LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              #  --  S band  --
              CH;     3263.794MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              CH;     3335.481MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              CH;     3349.193MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              #  --  C band  --
              OH;     4660.242MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              OH;     4750.656MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              OH;     4765.562MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              H2CO;   4829.6639MHz; LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              OH;     6016.746MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              OH;     6030.747MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              OH;     6035.092MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              OH;     6049.084MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              CH3OH;  6668.5192MHz; LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              OH;     7761.747MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              OH;     7820.125MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              #  --  X band  --
              OH;     8135.870MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              OH;     8189.587MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              3HeII;  8665.650MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              #  --  Ku band  --
              CH3OH; 12178.593MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              OH;    13434.596MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              OH;    13441.4173MHz; LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              H2CO;  14488.4801MHz; LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              #  --  K band  --
              SiS;   18154.888MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              C3H2;     18.343GHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              CH3OH; 19967.396MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              H2O;   22235.1204MHz; LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              CH3OH; 23121.024MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              NH3;   23694.4700MHz; LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              NH3;   23722.6336MHz; LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              NH3;   23870.1296MHz; LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              NH3;   24139.4169MHz; LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              NH3;   24532.9887MHz; LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              CH3OH; 25018.123MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              NH3;   25056.025MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              CH3OH; 25124.872MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              NH3;   25715.182MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              #  --  Ka band  --
              NH3;   26518.981MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              NH3;   27477.943MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              NH3;   28604.737MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              CH3OH; 36169.290MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              SiS;   36309.627MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              CH3OH; 37703.696MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              CH3OH; 38293.292MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              CH3OH; 38452.653MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              #  --  Q band  --
              SiO;   42519.375MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              SiO;   42820.570MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              SiO;   42879.941MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              SiO;   43122.090MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              SiO;   43423.853MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              CH3OH; 44069.476MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              CS;    48990.955MHz;  LSR; Radio;    0km/s; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              #  --  Only Redshifted lines  --
              DCO+;     72.039GHz; Topo; Redshift; 2.00Z; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              SiO;      86.243GHz; Topo; Redshift; 2.00Z; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              H13CO+;   86.754GHz; Topo; Redshift; 2.00Z; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              SiO;      86.847GHz; Topo; Redshift; 2.00Z; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              C2H;      87.300GHz; Topo; Redshift; 2.00Z; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              HCN;      88.632GHz; Topo; Redshift; 2.00Z; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              HCO+;     89.189GHz; Topo; Redshift; 2.00Z; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              HNC;      90.664GHz; Topo; Redshift; 2.00Z; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              N2H;      93.174GHz; Topo; Redshift; 2.00Z; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              CS;       97.981GHz; Topo; Redshift; 2.00Z; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              CO;      109.782GHz; Topo; Redshift; 2.00Z; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              CO;      110.201GHz; Topo; Redshift; 2.00Z; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              CO;      112.359GHz; Topo; Redshift; 2.00Z; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true
              CO;      115.271GHz; Topo; Redshift; 2.00Z; 10km/s; 5km/s; Dual; USE_RECIRCULATION=true