Orientation

The Advanced Search link (Figure 3.2) 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 calibrator at a position nearby your source of interest. This Advanced Search link will bring up a dialog box in the main editing window. In that window, select the catalog(s) in which the search should be performed, and select the table(s) with the required parameters by ticking the upper left tick-box of the relevant tables. On top you can quickly select All or None catalogs and subsequently toggle individual catalogs. Only when you tick a table, its options and editing fields become active. More than one catalog and more than one parameter table may be selected; the search interprets additional parameters as an AND condition. Be patient as searching can take a while; please do not continue clicking with the mouse button until the search operation has finished.

Figure 3.2: Web browser screen shot of the "Advanced Search" options with a filled in example of a cone search in combination with a minimum flux density.

A Cone Search searches a radius, entered in degrees, around a position (J2000). The resulting table should be sorted in increasing distance from the position, though you would want to check that; the table can be resorted if desired (by clicking table headers that can 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! For example, if you type 01 37 in the R.A. field, i.e., without indication of hour or minutes, you will see that it ignores the space and interprets this R.A. as 137 degrees (9h 8m) - funny eh? We're working on it.

Activating the Calibrator Code search allows to 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 the code that used to end up as the AIPS calibrator code (A, B, C, T), which is an indication of positional accuracy. Consult the VLA calibrator manual for more information on the definition of these codes and positional accuracies (http://www.vla.nrao.edu/astro/calib/manual/).

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 coordinate range, with the equal or larger than (>=), or equal 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 3.3: Web browser screen shot of results of the Advanced Search. Hovering with the mouse over structure (or flux or aliases) displays the calibrator list information (when available).

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.

Remember that a search automatically selects and switches to the Search Results catalog at the bottom of the search tool. 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 3.3). Except for the Advanced Search, previous searches are saved in this tree for convenience - navigating to a previous search is done by simply selecting that search. Note that a search will always change from the selected catalog to selecting the search results. Before performing another search in the same catalog, re-select the catalog! Sources presented in the search results - or the whole Search Results catalog - can be selected, and added to a personal source catalog using copy/paste, etc. To delete the results of a search, select the "Search Results" catalog in the search results tree and use EDIT - REMOVE SEARCH RESULTS form the menu strip.

Search results when using the Advanced Search are displayed in a table at the bottom of the page and added in the Search Results tree if it is sufficiently new (i.e., not started from the Search Results page). Following searches, when not leaving the Advanced Search tool, will overwrite the current table with the new search results. Search results are cleared when you log out from the OPT web application.

Select the VLA source catalog. Source names follow IAU naming convention and aliases can be found by hovering over aliases, or by viewing the source properties (through the editing icon ). To find source 3C286 may take a while, even if you know this source is J1331+3030 in the IAU convention. Entering 3C286 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. 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 3C286 or skippy, etc); it then will only find this source in the VLA source catalog if J1331+3030 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), for example in the VLA catalog, 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 tick box ticked. A search on 1331+ will return 3C286 (as J1331+3030). Searches are not case sensitive. 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* (and an empty search string thus 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 data base, using the same search and character rules.