Orientation and Working with Catalogs in the OPT

by Gustaaf Van Moorsel last modified Mar 16, 2017 by Lorant Sjouwerman

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.