These instructions presume a working knowledge of Aips. Please refer to the Aips Cookbook for detailed instructions on running the tasks.
Before starting Aips, create a directory for the date of the polcal observation; e.g., 20040524. Copy the scripts to and run Aips from this directory.
polcal = the calibrator with the most scans around 30 degrees
phacal = all calibrators except abscal and weacal
weacal = any calibrator with flux of less than 1 jy
strongcal = any calibrator with flux of more than 10 jy
abscal = 3C48 (0137+331) or 3C286 (1331+305)
absref = reference antenna
numcal = number of phacal calibrators
From the Tip Curve Data Tool, select the year of data, band and the observation date on which the polcal data was taken.
Find the "fitted zenith opacity" on the data page. This is a percentage and should be entered in the script as the correct value; e.g., 7.1% = .071
| version 'online' | Be sure the correct device is mounted |
| nfiles 0 | 0=today; -x for number of previous days, up to 13 |
| vlaobs 'polca' | |
| timer | Set time range for which observation was run |
| bparm(1)=-1 | No opacity |
| bparm(2)=1 | Use Aips gains |
| cparm 8=10/60 | Use 10 second intervals |
From the NRAO Data Archive System, download the data to a disk file. Use the above parameters in FILLM with the following exceptions:
| nfile 'filename' | where filename is the name of the downloaded file. If the final quote is omitted in filename, the case is preserved. Aips adds a 1 to the end of the filename. | timer 0 |
| vlaobs '' | |
| docat=1 | If the archive file spans two files, user docat=1 to append the second file. |
| ncount=x | Where x = the number of files to read. |
| optype 'scan' | Lists each scan with time and source name |
| docrt 1 | Print results on screen |
| version '' |
| opcode 'beg' | Beginning |
| aparm 0 10/60 | Quack first 10 seconds |
| sources '' | All sources |
| TVFLG Parameters | |
|---|---|
| tvcl; grcl | Clear data and grid on TV |
| default tvflg | Restore defaults |
| dparm(6) 3.3 | Set flagging rate |
| stokes 'rrll' | All stokes |
| flagver 1 | Flag table version 1 |
After TVFLG is running, enter stokes '1111' and switch all IF. Use tvfiddle to set up zoom and dynamic range.
| restore 0 | Resets all parameters |
| version 'pwd' | Run from current directory |
| run calb? | Where ? is the band designator |
| setit | Sets up script defaults |
| dowait 1 | Stop at first error |
| calgain(i) | run for K & Q only, where i is the file number from Aips |
| caldata(i) | |
| listcal(i) | Check amplitudes (see below) |
| calpol(i) | |
| outpol(i) | Runs imagr; this takes several minutes |
*.PCAL files show the polarization leakage. This should be within a few degrees or less (.01 or .02) at C band. K should be less than 0.10. In Q, the error should be less than the leakage.
Polarization leakages greater than maximum indicate antenna problems which should be reported to the front end group.
*.POLC are the residuals. One antenna will be off in phase for a bad leakage calibrator. The gain should be ~3xxx and consistent. A high number equals low amplitude and may indicate that more flagging needs to be done with the data.
*.TXT are summary files. Use the command:
The data are summarized into html format through a group of Perl scripts. The scripts should be located in your higher level directory and the data located in sub-directories with the format yyyymmdd; e.g., 20040101.
calgen.pl yyyymmdd
This will create the html files within the sub-directory yyyymmdd. A separate file will be created for each calibrator.
calextract.pl
This will create a summary html file which you can view with any web browser:
master.html (all bands)
X_band.html
C_band.html
K_band.html
Q_band.html
These files may then be transferred to the web page:
/home/nraoweb/vla/content/astro/calib/polar/YYYY/yyyymmdd
Transfer all *.html, *.CALIB, *.TXT and the Aips scripts which were run to produce the data. It is also
a good idea to archive the data with fittp and transfer that archived data to the web directory. This insures
the data could be recovered if needed.
Aips has no way to change directories without first quitting Aips and restarting. Each set of scripts and data must be contained in a unique directory with the name format of yyyymmdd.
Typos, especially in the source names, create havoc with Aips. If you get any unusual errors, first check the names of all sources.
Sometimes, imagr files are left on indisk 2. Do an mcat and delete all imagr files before running outpol.
This can make Aips looks like it's gone insane, plus make Eric really mad at you for doing such a foolish thing and then asking for help.
The result is that Aips will not stop at the first error. By the time it gets confused enough to stop, you have no idea what really went wrong.
Old parameters may be left over from previous scripts or other functions in Aips.
With interruptions, it's easy to forget where you are, either within a day's calibration, or within a band. It is a good idea to keep a log of what's been done.
Forgetting to change numcal to match the number of calibrators really sends Aips off into never-never-land. Double-check this number before running the script.
After a script has been modified, it must be rerun. First, restore 0, then run the script. It is easy to forget to rerun the script after it has been corrected.
If one antenna has very high gains, this throws the rest of the antennas off, making the flux look higher than normal. This may not be evident in tvflg. Run listr with optype 'gain' to check for very high gains in one antenna.