VLA/VLBA Polarization Previous News
Steve Myers & Greg Taylor
Last update: 26 May 2005
- The K-band subreflector rotations have
been reoptimized as of Mon 13 Jan 2003, so current posted gain curves are
invalid. See note on the Gain Curve Page.
- A list of VLA memoranda dealing with polarization issues is
available here. This is somewhat out of date and unfortunately
most memoranda are not available on the web, only in hardcopy form
at NRAO libraries. (2002-9-18)
- Models are now available for 3C138 (0521+166)
and 3C147 (0542+498) at U, K and Q bands in the
Image Archive in addition to those for 3C48 and 3C286.
These are FITS images with clean-components tables on the 1999.2 flux scale,
courtesy Claire Chandler.
See Claire's Page
A record of the VLA d-terms culled
from the PCAL output from the calibration runs is
now available here. Beware, as changes due
to antenna moves, reference antenna changes, and receiver changes have
not been taken into account. Note also that these have been computed
before the R-L phase differences were calibrated using 3C48/3C286.
Still, these may be of interest to check if your solutions are reasonable.
Upon request, I can provide the data files from a given run so that the
AN table can be copied to apply these d-terms to your data.
The latest versions of the RUNFILEs
that load the automatic AIPS procedures are available
Updated Q, K and U band gain curves
are now available from the
VLA Gain Curve Archive Page.
Note that the new November 2001 gain curves supersede
the curves from October 2000 and should be used especially for K and
Q band data taken June 2001 onwards.
Data from 2002 is now available, and should have the correct gain
and opacity corrections. Note that now all frequency bands are on the
1999.2 flux scale. The session reports are now available for
2002 along with the previous
Tables and Plots now available split by year. A
one-month overlap with adjacent years is built into the tables and plots.
WARNING: The K and Q data starting from
21-SEP-2001 will have had gain and opacity corrections applied twice.
I don't see anything visible in the plots, but I will be redoing these.
NOTE - In the AIPS versions 31DEC01 and later,
FILLM will by default apply gain curves and approximate opacity corrections,
and thus you should not use manual gain curve corrections unless you defeat
these (check BPARMS). You can check your CL 1 table to see if you have
this problem also. If so, you can delete CL 1 and remake it with INDXR
to start over with unity gains.
If you want to use TIP curve derived opacities in CLCOR,
set BPARM(1)=-1 to turn off the automatic application of WX-based opacities
when using the 31DEC01 or 31DEC02 AIPS. Because the WX opacities are not very
accurate, and are time variable over the run, I do not recommend using these
at this time if better TIP data is available. I will investigate this
Note also that there seems to be a problem
with the flux densities referenced to 0137+331 from 20001022 to 20010623
(see 2355+498 Kband) - I will try
to chase this down. (2002-1-11)
Starting with the C-config
2001-07-02 calibration runs, we are using the new (1999.2) flux density
scale and Claire Chandler's models for 3C48 and 3C286 at K and Q band (see below). You will note a jump in the flux scale,
especially for sources indexed to 3C48, at this point in the archive. We
will back-propagate this calibration as soon as we can. (2001-7-27)
- On 8 June 2001 (1600 UT), optimization was carried out for the
installed Q-Band systems taking into account
proper subreflector rotation for the feed locations of the receivers.
As a consequence of this, AN 2, 21 and 26 should look better at least at the
nominal elevation of about 50 degrees. All other antennas, with the
exceptions of AN 3, 4, 6, 8, 12, 13, 14, 16, 22, and 27 (which had already
had this rotation trick applied) will see improvement at extreme elevations
and flatter gain curves in general. Unfortunately, this means the
previous gain curves for all but AN 3, 4, 6, 8, 12, 13, 14, 16, 22, and 27
will now be invalid to some extent. We will try to obtain new gain curves
soon but until this time you may find that the old gain
curves will no longer work well. (2001-6-14)
Claire Chandler is producing better
K and Q band models for primary calibrators 3C48 (J0137+331) and
3C286 (1331+305) in A-configuration and A+B configurations.
You can download these FITS models
calibration web page. Available models:
Note that these models are calibrated to the
new flux scale. (updated 2001-4-30)
VLA images and clean models for 3C48 and 3C286
from this past A configuration are available
here. The were calibrated using the old
flux density scale - the scale was updated in Dec 2000 and eventually we will
update the database to use this.
VLBA Scientific Memo 26 detailing this program is now
VLBA images of selected calibrators
are now available - see below (2000-9-22)
Plots of individual source fluxes
and polarization now available from tables (2000-9-11)
Of course, there is the main
Calibration Manual and
If you have scheduled tipping scans in order to determine
atmospheric optical depths, you can find the results on
Bryan Butler's Tip Scan Archive page.
The results of these calibration runs, in addition to providing
information on source polarizations and fluxes, serves to check the
performance of the VLA antennas. After each calibration run, a report
is generated and sent to VLA antenna and correlator personnel. There
archive of performance and reduction reports by session
(since March 2000) available for browsing.
Thursday, 02-Sep-2010 17:00:35 MDT