Orientation

Catalog Tables in the RCT and the SCT

Click NRAO defaults in the left-hand side column to return to the NRAO defaults catalog. The table at the top of the main RCT editing or manipulation window (Figure 2.2) has a header line with obvious meanings. (If not, we should have supplied a fly-over help tool-tip for it; the tool-tip help shows up when the mouse hovers over the item for a second or so.) When you move the mouse over the headers you will see that they switch color to orange. Every table column with a header showing this behavior can be sorted by clicking the header. This is so for all other tools as well. A table with more than 25 entries may span multiple pages, but this catalog currently is too short to demonstrate this (see section 3.1.1). 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).

OPT figure 2.2

Figure 2.2: Web browser screen shot of the RCT when NRAO defaults is selected.

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 ( $\includegraphics[height=3mm]{psimg/source.png.ps}$ ). The tick-boxes can be used to select one or more entries in the catalog for copy/paste as described in the next 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 has to be redone for every page. The $\includegraphics[height=3mm]{psimg/source.png.ps}$ edit icon is used to access the details of the resource entry in the catalog, i.e., the specifics of the hardware and instrument configuration.

Show and Edit Catalog Entries in the RCT and in the SCT

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.. Of the OSRO resources, this would be OSRO1: 256 MHz total bandwidth, delivered in two 128 MHz chunks. As an example of a continuum OSRO1 resource, click on the ( $\includegraphics[height=3mm]{psimg/source.png.ps}$ ) edit icon (with fly-over help tool-tip Show/Edit properties for this catalog entry) in front of the C band resource to see the user selectable hardware and instrument options used in this resource. To get to C band when NRAO defaults is highlighted, navigate through the table, or select group 2x 128 MHz Full pol (OSRO1) in the left hand side column to remove clutter from pointing setups first.

The information displayed (figure 2.3) is the receiver selection in the table on the top (C band; 4.0 to 8.0 GHz), followed by the OSRO mode (here OSRO1; Full polarization, two subbands, 64 frequency channels). Next follows a table with the center frequency setting for two output pairs^2.1(centered on a sky frequency of 4896 and 5024 MHz, where a pair consists of RCP and LCP signals). Finally, information on the correlator integration time (3 seconds), the subband observing bandwidth (128 MHz per output pair) and the frequency channel width (2.0 MHz, which is 128 MHz divided in 64 frequency channels each).

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 2x 128 MHz Full pol (OSRO1), 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.

OPT figure 2.3

Figure 2.3: Web browser screen shot of the OSRO1, full polarization C band resource.

Introduction

The resources for continuum (and spectra-polarimetry) OSRO1 observations and for spectral line OSRO2 observations are very similar and the differences will vanish with further commissioning of the WIDAR correlator. For now, they will be discussed separately below, but remember that all data is delivered in frequency channels. The resources in this NRAO defaults catalog are read-only, as indicated by the slanted red font, and selections are hard coded. Entries therefore appear slightly different from entries in a personal resource.

Spectral Line Resources

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 form, meaning that the continuum resources described above are already spectral line resources. However, when the scientific interest is in a specific line, typically one would want to use a spectral resolution that is better than the spectral resolution 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. Currently, during the OSRO period, there are two possibilities to do this, depending on the requirements on polarization and width of the frequency channels:

For polarization measurements all polarization products are needed. The correlator must be configured as OSRO1, centered at the anticipated observing frequency. The total number of frequency channels is 128 (twice 64), and the frequency channel bandwidth can be selected to be from 2.0 MHz, in steps halving the width, down to 488 Hz. The total bandwidth will be twice 64 times the channel width.

If total intensity (Stokes I) is sufficient, the correlator may be configured as OSRO2, centered at the anticipated observing frequency. The total number of frequency channels is now 256, and the frequency channel bandwidth can be selected to be from 0.5 MHz, in steps halving the width, down to 122 Hz. The total bandwidth will be 256 times the channel width.

The difference in correlator configuration between OSRO1 and OSRO2 is that giving up one output pair and giving up the cross polarization products from OSRO1 each doubles the frequency channels available in OSRO2. However, if the science requires the simultaneous observation of two lines separated by more than the total bandwidth of the single output pair, the observations must be done using OSRO1 and the trade-off is using less channels per line or using a coarser spectral resolution. For example, simultaneously observing the SiO lines at 42.8 and 43.1 GHz would require OSRO1, the continuum resource^2.2.

Note that at the moment Doppler calculations using a rest frequency is disabled. Check section A.3 for more information.

Example of a Resource Catalog: the NRAO defaults catalog

The NRAO defaults catalog (Figure 2.2) 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 continuum observations in the early EVLA era, i.e., using the receivers and correlator available to the observers during the OSRO program. These defaults are mostly useful for OSRO continuum bandwidth observations. They differ from the previous VLA NRAO defaults in frequency mainly because a larger instantaneous bandwidth is available: 256 MHz now versus 100 MHz before. The EVLA also has new and extended range receiver bands.

Note that NRAO defaults is in red italics, which means that this catalog is read-only. The plus-icon ( $\includegraphics[height=3mm]{psimg/expand.png.ps}$ , Figure 2.1) in front of the open book icon ( $\includegraphics[height=3mm]{psimg/book_open.png.ps}$ ) indicates that this catalog includes sub-catalogs which are referred to as groups. A catalog does not need to contain groups, but at some point it may be more convenient to have them. If you click the plus-icon or NRAO defaults these groups will appear in the catalog tree and the plus-icon will change to a minus-icon. If you clicked on NRAO defaults, you will also see a table of contents of the highlighted NRAO defaults catalog in the main RCT 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). Groups are, in this case, 2x 128 MHz Full pol (OSRO1) and Pointing setups. When highlighted or selected using the mouse button, the right-hand side window with the table of contents will only show (filter) the resources which were grouped in this sub-catalog. For example, selecting the 2x 128 MHz Full pol (OSRO1) group will now only list the NRAO default resources for continuum observations. Similarly, the Pointing setups will show the NRAO default resources for pointing scans in X, K, Ka and Q band (see below).