Computation

            

1. BPASS also comes replete with a vast set of adverbs, so I have also provided a subset of them, at the cost of some flexibility, in the procedure ATBPASS. Once again, it is recommended that you look briefly at BPASS to ascertain the differences. The main change is that in BPASS, you can divide the visibilities by a model, but in ATBPASS you can't. In addition, division by channel 0 is optional in BPASS, in ATBPASS it is enforced. Here follows a description of some of the ATBPASS adverbs.
   • inname, inclass, inseq, indisk. Fill these in as usual with GETNAME on the slot containing the spectral data base.
   • calsour selects the sources to use for the bandpass calibration. You may include more than one source if so desired.
   • calcode is the calibrator code for easy selection (for example, perhaps you set calcode='bp' for the bandpass calibrators with SETJY).
   • timerang allows you to select some subset of the bandpass calibrators in time.
   • bchan, echan allow you to determine the response for some sub-portion of the band. The procedure can be very time consuming for big data bases and this may prove useful.
   • solint allows you to specify the solution time interval. -1 means average over all times (you should probably not use more than one source if you use this option, although you might get away with it because of the `divide by channel 0' option) and 0 means do a scan average. Otherwise, it is the time in minutes.
   • refant should be set to the same one that you used in ATCALIB or CALIB, but it is not vital.
   • in3name, in3class, in3seq, in3disk refer to an external channel 0 data base such as that produced by AVSPC. If in3name etc. is not filled in, then the channel 0 visibilities will be formed from the central 75% of the band. The channel 0 division is always performed in ATBPASS, one way or the other.
2. Set ATBPASS in motion with GO ATBPASS and let it grind away. You should run ATBPASS once for each freqid and write a new BP table for each case.

   inname,inclass,inseq,indisk Fill in for spectral data base

   calsour=' ' Select bandpass calibrator(s) explicitly

   calcode='bp' or with calcode

   uvrange=0 Select full uvrange or set in klambda

   timerang=0 Select all times

   freqid=1 One freqid per run

   bchan=0 Select all channels or specify subset echan=0

   solint=-1 Average all times or

   solint=0 Scan average or average

   solint=30 for 30 minutes

   refant=3 Select the same ref. antenna as in CALIB

   bpver=0 BP table version to write

   in3name,in3class,in3seq,in3disk Fill in for channel 0 data base or leave blank to use central 75% of band

3. After ATBPASS completes, you should examine the bandpasses. This can be done with POSSM. Almost all the inputs to POSSM can be ignored for this purpose. Just make sure that aparm(8)=2 (plot the BP table) and bpver points at the desired BP table. Depending upon the solint used when you ran ATBPASS, there may be one or more time entries in the BP table. Use the timerang adverb to select which entry you would like to see (for example, to see the temporal stability of the bandpasses), or leave it at 0 to average them all. Make one plot for each of the N antennas by running POSSM N times, selecting the desired antenna with antennas. If you select all antennas in one go, you get a bandpass averaged over them all. You can display the plot directly on the TV with POSSM by putting dotv=1, or display the plot file created (dotv=-1) with MIXPL, TKPL, or TVPL. The antenna that you picked as the reference antenna should have zero phase across the whole band. Make sure also that the amplitude scale is sensible and that the response peaks at a value close to unity.

   bpver=0 Highest BP table version

   aparm(8)=2 Plot BP table.

   antennas=3 Plot response for antenna 3 say,

   antennas=0 or all antennas averaged together

4. You can also check that the application of the band-passes to the data is working correctly. Do this with POSSM as well. However, instead of asking it to plot the BP table, you ask it to apply the BP table to the data and plot a spectrum.
5. You can also check that the application of the band-passes to the data is working correctly. Do this with POSSM as well. However, instead of asking it to plot the BP table, you ask it to apply the BP table to the data and plot a spectrum. In the example we plot a single baseline of the primary calibrator with the calibration and bandpass corrections applied. We vector average and since the source is a point source in the phase centre, we get a strong signal.

   inname,inclass,inseq,indisk Specifiy multi-source file

   source='1934-638','' Specify source of interest

   antennas=1,2 Select baselines of interest

   docalib=1 Calibrate data with

   gainuse=2 CL table 2

   doband=1 Calibrate data with

   bpver=1 BP table 1

   aparm(1)=1 Vector average

   solint=-1 Scan average

   dotv=1 Plot on TV

Last update : 27/11/93

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