Sources

by Gustaaf Van Moorsel last modified Jul 01, 2017 by Lorant Sjouwerman

The Sources section is used to enter the positions and velocities/redshifts (where relevant) of your target sources. As of the 1 February 2013 deadline the NRAO now requires proposers to specify their source lists in full. This enables the Observatory to identify potential conflicts between observing programs and to better understand scheduling pressure on the instruments it operates. It may be the case that the final target list has not been selected at the time a proposal is submitted. In such cases, all potential targets and fields should be listed. The only exceptions to this requirement are for Triggered proposals to observe targets that are unknown a priori. Proposal source lists are not made public by the Observatory. For some types of observations, knowing the calibration source is important for evaluating the technical justification, and the calibration source should be included in the source list.  Calibration sources may be included for all types of observation, but their inclusion is not required.

There are three different ways to do this. You can (1) enter the information by hand, one source at a time; (2) search for source information from NED/SIMBAD; or (3) load source information from a local data file.

Merely adding a source in the Sources section does not ensure that time is requested to observe that source. The source must also be paired with a telescope resource, and that source-resource pair must be added to a session (see the Introductory Sources, Resources, and Sessions Section and the Section on Sessions).

Source Groups

Source groups are intended to make it easier to handle observations of a large number of sources within a single observing session. The source/resource pairs which form the basic units of observing sessions (see the Introductory Sources, Resources, and Sessions Section and the Section on Sessions) refer to source groups. Click on the New Source Group'' button to add a new source group. A single source may belong to multiple source groups. We provide examples of how to use groups for the GBT and for the VLA.

 

Adding Sources by Hand

Once a group is created you can add new sources by hand by clicking on the Add'' button, then entering the appropriate information in the entry fields.

For the VLBA/HSA or GMVA, if multiple fields are to be correlated for some or all pointings, the source positions entered should be the desired pointing centers, and the Scientific Justification should make clear the selection criteria for which sources will be correlated within a given pointing. See §2.3.6 for more details on multiple-field correlation.

The entry fields for adding a new source include:

  • Source name: A unique name for the source. This should be less than 60 characters long.
  • Coordinate System: The only coordinate system available at this time is equatorial.
  • Epoch: The epoch for the coordinate system used to define source positions. Only J2000 or B1950 are currently allowed. The default is J2000.
  • Longitude center: The longitude coordinate (e.g., right ascension) of the source or the reference position for a multi-point map, specified as hh:mm:ss.
  • Latitude center: The latitude coordinate (e.g., declination) of the source or the reference position for a multi-point map, specified as dd:mm:ss.
  • Longitude range: The longitude coordinate range (±) used for multiple-pointing mapping, specified as hh:mm:ss. Should be 00:00:00 for single-pointing observations.
  • Latitude range: The latitude coordinate range (±) used for multiple-pointing mapping, specified as dd:mm:ss. Should be 00:00:00 for single-pointing observations.
  • Velocity reference frame: The options for the velocity reference frame will depend on those available for the different telescope control systems. VLA/VLBA: Barycentric, LSRK, or Topocentric; GBT: Heliocentric, Barycentric, LSRK, LSRD, Topocentric, Galactic, or CMB. The default is LSRK.
  • Velocity convention: The velocity convention may be: Optical, Radio, Relativistic, or Redshift. The default is Radio.
  • Velocity: If the velocity convention is either optical, radio, or relativistic then the this value is the velocity of the source in km/s; while if the velocity convention is redshift then this value is the redshift (z) for the source. The default is 0.0.
  • Calibrator: A checkbox indicating whether or not the target will be used for calibration purposes. The default is n.''

 

Once the source information is entered, click the Save'' link. A message will report either that the source was successfully added, or that some error was found. In the latter case the offending entry or entries will be pointed out; simply correct those entries and press the Save'' link again. The source will now appear in the source table on the Sources section. Note that a source which is a member of multiple groups will appear multiple times in the source table.

 

Find Source in NED/SIMBAD: Searching For Sources

You can search NED and SIMBAD for source information if you know the object's name. Click on the Search NED/SIMBAD'' button; then enter the object's name (e.g., B0329+54) in the Target Name'' field and press the Search'' button. You will then be presented with the result of the search. The search currently goes through NED and SIMBAD, and names should adhere to their conventions (e.g., GRS 1915+105, NGC 4500, M31, HD19688). Only the most direct match is returned; that is, no extended name search is done. For example, M31 returns M31, not Mayall II, etc.

 

Load Sources From File: Reading in a Source List from a File

N.B., the format has changed twice: for the 1 February 2010 deadline and for the 1 February 2013 deadline. Click the Convert'' button to convert the most recent old format to the new format. For the 1 August 2013 deadline we use yY/nN instead of true/false for the calibrator flag but both formats are accepted in the input file.

You can read in some or all of your sources from a local ASCII file that you have edited offline from the PST. Click on the Import'' button to view the browse/load options. To load the contents of the file into the PST, first enter the path and name of the file into the Source Data File'' field, either by hand or using the Browse'' button, and then click the Load'' button.

This ASCII file must be formatted as follows:

Source Name; Group Names; Coordinate System; Epoch; Longitude; Latitude; Reference Frame; Convention; Velocity; Calibrator;

The delimiter is the semicolon (;) character. A delimiter must be present for every field. Since there are ten fields, each line in the text file must have ten delimiters. There must be a carriage return at the end of each line. If a line starts with the number symbol (#) or a star (*), the line will be ignored--that is, this line will be treated as a comment. N.B., the longitude and latitude coordinates must use sexagesimal units (e.g., hh:mm:ss and dd:mm:ss). Here is a simple example:

NGC3242; PNe; Equatorial; J2000; 10:24:46.1; -18:38:32; Barycentric; Optical; 4.70; n;

White space (e.g., space character, tab character) at the beginning and end of a line is permitted but will be ignored. Likewise white space immediately preceding or following the delimiter is also permitted but will be ignored. White space within a field, as in a b c'' is preserved. For example, the following two lines will be handled identically by parsers:

NGC3242 Pos1 ; PNe ; Equatorial ; J2000 ; 10:24:46.1 ; -18:38:32 ; Barycentric ; Optical ; 4.70; n;

NGC3242 Pos1;PNe;Equatorial;J2000;10:24:46.1;-18:38:32;Barycentric;Optical;4.70;n;

Optional fields are permitted and include Group Names, Coordinate System, Epoch, Reference Frame, Convention, and Velocity. An optional field may be left unspecified. For this purpose unspecified means either that there are no characters present for that field, leading to consecutive delimiters (e.g., ;;''), or that the only characters in that field are white space characters (e.g., ; ;''). The following example shows the minimal amount of information that must be specified:

NGC3242;;;; 10:24:46.1 ; -18:38:32;;;;;

Some fields are allowed to hold multiple values. The comma (,) character will be used to separate the multiple values. The same rules regarding white space apply here as in between fields--i.e., white spaces immediately preceding or following the value delimiter is ignored. The comma after the final value is not mandatory. For example, the following lines all represent the use of multiple values in the second field and will be handled identically by parsers:

NGC3242 Pos1; G1, G2, G3; Equatorial; J2000; 10:24:46.1; -18:38:32; Barycentric; Optical; 4.70; n;

NGC3242 Pos1; G1, G2, G3,; Equatorial; J2000; 10:24:46.1; -18:38:32; Barycentric; Optical; 4.70; n;

NGC3242 Pos1;G1,G2,G3; Equatorial; J2000; 10:24:46.1; -18:38:32; Barycentric; Optical; 4.70; n;

 


Modifying Source Groups

To modify a source group click on the group name. Rename a source group by editing the text field and clicking the Save'' button; click the Delete'' button to delete the group; or click the Cancel'' button to cancel. To modify sources within a source group a similar procedure is used, except now click on the source name located with a source group table. The different attributes of a source (RA, Dec, etc.) may be edited and then saved. Both sources and source groups may be reordered using the up/down links.

NOTE: When deleting source groups that are included in a session the PST will warn you that by deleting the source group the session will also be deleted. At this point you can either proceed with this operation or cancel.