CORRECTING THE FLUX DENSITY SCALE OF SECONDARY CALIBRATORS

                 

 

Before applying the antenna solutions to the program sources, you must set the flux density scale correctly. So far, via SETJY, you have set the scale for the primary calibrator only. When ATCALIB worked out solutions for the secondaries, it assumed a flux density of 1 Jy for each of them (unless you had entered a value into the SU table or already done a round of ATCALIB and GETJY). Now the solution amplitudes for the primary and secondary calibrators stored in the SN table can be ratioed to work out the secondary calibrator flux densities. The task GETJY is used for this purpose.

• Select the list of secondary calibrators with the sources and soucode adverbs. If you have a lot of secondaries, it is quicker to leave soucode blank and select them only with soucode (provided you used SETJY to give the secondaries a calcode).
• Select the primary calibrator with calsour and calcode.
• You may need to set the uvrange, antennas, freqid, bif, and eif combinations in the same way that you did when running ATCALIB and run GETJY several times.
• You may also find it necessary to set a time range with timerang. For example, if you have observed at low elevations and at a high frequency, the calibrator will probably have been attenuated by the atmosphere and the gains will come out appropriately bigger. Ideally, you should use secondary calibrator scans at the same elevation and close in time to the observation of the primary calibrator. In practice, you can only approximate this requirement.
• You can select a specific SN table with snver, or select all SN tables by leaving it at zero. If you select a specific SN table, then gain solutions for the primary and secondary calibrators must be contained in it. It may be necessary for you to delete specific SN tables before running GETJY if you want most of the available tables.

  sources='0123-23','1322-45',' ' Select secondary calibrators by name

  soucode='s' and/or with source code

  calsour='1934-638',' ' Select primary calibrator by name

  calcode='p' and/or select with calibrator code

  qual=-1 Select all qualifiers

  bif=1 Select IF range

  eif=2 of interest

  timerang=0 Select all times

  antennas=0 Select all antennas

  freqid=1 One run per freqid

  snver=0 Select all SN tables or specify

• Following computation, GETJY enters the new secondary calibrator flux densities into the source (SU) table and reports them to the user as well. In addition, GETJY corrects the solution (SN) table(s) to account for the newly determined flux densities of the secondaries.

Last update : 27/11/93

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