AIPS files generally have a number of tables associated with them which contain ancillary information about the file. In this Appendix I will describe briefly what the most common tables you will encounter are for. The AIPS command IMHEAD\ will enable you to see which tables you have associated with a file and you can list the contents of these tables with the task PRTAB.
PRTAB | |
inext='FQ' | Select table type, FQ for example |
inv=0 | Highest table version |
xinc=1 | Print all rows |
docrt=-1 | List on printer |
docrt=132 | List on terminal, 132 char per line, must |
switch terminal to 132 char output too | |
dohms=1 | HH MM SS times instead of decimal days |
You can have many versions of CL tables, and select the appropriate one with the adverb gainuse. For ATCA data, CL table 1 is a pristine copy with values appropriate to ideal gains. It is created by ATLOD. You should not delete this pristine version, but if you do, you can regenerate it with the task INDXR.
The gains are stored in the CL table at time intervals generally of the order of minutes (although the integration time might be seconds). They are arrived at by smoothing and interpolating the gain solutions stored in the SN table with the task CLCAL or the procedure ATCLCAL.
Note that CL tables are cumulative. This means that when you generate a new CL table, you always do it by first reading a previous version CL table (selected with adverb gainver), apply the gain solutions in the desired SN table (selected with adverb snver) to it and write out the new CL table (selected with adverb gainuse). In this way you can incrementally build up a better and better calibration which is useful for self-calibration applications (see § 17).
Each different group of simultaneously observed frequencies (such as the two simultaneous IFs you get with the ATCA) is designated by an integer number (the FREQID). Each FREQID has one logical row in the FQ table. For each simultaneous frequency (IF) contributing to the FREQID, the logical row has an offset in Hz from the reference frequency in the header, a channel width, a total bandwidth and a sideband indicator. Thus, the logical row is multi-dimensional; there are as may actual rows in the logical row as there are simultaneous frequencies (IFs).
If you observed, say, at 3 cm (IF 1) and 6 cm (IF 2), and then changed to 13 cm (IF 1) and 20 cm (IF 2), you would get two FREQIDs in the FQ table. The first would describe the 3/6 combination, the second the 13/20 combination.
You select the desired FREQID in the FQ table with the adverb freqid.
For tortuous historical reasons, the channel width is now a signed quantity, and the sideband indicator is now always written as +1. The true sideband indicator is written to the screen when you load your data with the task ATLOD. It is also written into the history file if you forget it. It varies from band to band.
Occasionally you may come across CH tables. These are old deprecated versions of the FQ table. The FQ table is created by ATLOD. Do not delete it or you will have to make a new one with ATLOD.
Last update : 27/11/93
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