Example of a Source Catalog: the VLA (calibrator) catalog

The VLA catalog is the VLA calibrator list, a collection of radio sources also available in the Jobserve (and observe) VLA scheduling software. Browsing this source catalog is instructive to become familiar with the information available for sources. 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 RCT tool. The source search tool is an extra feature, and the presentation of information in the main editing window differs from the RCT due to the use of page tabs (see below).

The VLA source catalog is in red italics and has a plus-icon in front of it. You know this means that this catalog is read-only and has groups. If you click the plus-icon or VLA these groups will appear in the catalog tree, and you will see that the RA Groups and Dec Groups also have (sub)groups. Clicking VLA 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 source J0001+1914. At the bottom (or top) of the table (you may need to scroll down, e.g., using the window scroll bar), you will notice that the bottom line is a small page navigation menu. A similar page navigation menu can be found at the top. This VLA catalog contains more entries that fit on the page (25), and in this case is distributed over many pages. The menu icon buttons mean, from left to right:

	first page of the catalog (or group)
	10 pages backward in the catalog (or group), or as many as possible if less than 10 exist
	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
	next page in the catalog (or group)
	10 pages forward in the catalog (or group), or as many as possible if less than 10 remain
	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, 200) on the top of the page. Every table column with a header turning orange when the mouse hovers over it can be sorted on using a click of the mouse button (like in the RCT tool). 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 the catalog has 75 pages! Using the table header sort, confirm that the source with the most southern Declination is J1118-4634. Hovering over flux, structure 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. 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, e.g., Galactic, the positions are recalculated from the positions entered originally, which is indicated by a small red asterisk next to the coordinates.

Select a random source (not J1118-4634) and expose the source details (in the table, click on the editing icon before 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, Image Links and Notes. Each of these tab-pages has groups of information divided by a gray horizontal bar. 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). Another useful piece of information is in the Notes tab, under Notes. Press the blue circle with the white triangle/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.

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.