2.2. Monitoring of Flux Density Calibrators
Since the planet Mars and 3C295 are too heavily resolved for most VLA
observing programs, the flux density of a small set of calibrators is
carefully measured with respect to 3C295 and Mars in the 'D'
configuration every few years. These more compact sources have been
found to be only slowly variable (with some exceptions at the highest
frequencies). Below we provide the current (1999.2) best analytic
expression for their flux densities.
Log S = A + B * Log v + C * (Log v)**2 + D * (Log v)**3
where S is the flux density in Jy and v is the frequency in GHz. These
expressions are valid between 300 MHz and 50 GHz.
Source A B C D
3C48 1.31752 -0.74090 -0.16708 +0.01525
3C138 1.00761 -0.55629 -0.11134 -0.01460
3C147 1.44856 -0.67252 -0.21124 +0.04077
3C286 1.23734 -0.43276 -0.14223 +0.00345
3C295 1.46744 -0.77350 -0.25912 +0.00752
The 31DEC99 version (with the proper patch installed) of AIPS program
SETJY with OPTYP = 'CALC' will calculate and insert the flux densities
based on the above expression and parameters into a VLA database.
Alternatively SETJY can be told to use the old Baars et al (1977)
expression and parameters (see previous section), or the 1995.2,
or 1990 coefficients. AIPS Versions
15OCT89 through 15JAN96 use the 1989.9 coefficients or the Baars
coefficients. With versions of AIPS prior to 15OCT89 the flux density
of the calibrators must be set with OPTYP = ' ' for each IF. Do not
use SETJY with optype 'CALC' if you are switching frequencies within
the observing run. In this case you must calculate and insert the
appropriate values for each frequency and IF with OPTYP = ' '. You
may find it more convenient to split the databases into single FQid
components.
Observations taken prior to 1990 may benefit from using
the adjustments below when setting the flux density of 3C48, 3C147 or
3C286. Below are listed the RATIOS between the true and Baars et
al. value for 3C48, 3C147 and 3C286 at the various frequency bands
from 1983 to 1995. Multiply the Baars et al. value by this ratio to
obtain the correct flux density. Contact R. Perley or G. Taylor if
you need more information.
1983.5 1985.5
L C | L C U
----------------------------------------|-------------------------------------
3C48 1.004 1.039 | 1.018 1.047 1.11
3C147 0.974 0.957 | 0.970 0.948 0.99
3C286 0.995 1.010 | 0.993 1.002 0.99
1987 1989.9
P L C X U | L C X U
----------------------------------------|-------------------------------------
3C48 0.95 1.02 1.04 1.06 1.10 | 1.019 1.043 1.049 1.076
3C147 1.00 0.97 0.95 0.97 1.01 | 0.975 0.951 0.949 0.993
3C286 0.95 1.00 1.01 1.01 1.02 | 0.999 1.005 0.995 0.991
1995.2 1999.2
P L C X U P L C X U
----------------------------------------|----------------------------------
3C48 0.948 1.017 1.023 1.034 1.034 | 0.966 1.016 1.008 1.009 1.004
3C147 0.990 0.983 0.974 0.999 1.046 | 0.998 0.984 0.987 0.975 1.002
3C286 0.971 0.999 1.008 1.006 0.988 | 0.967 0.999 1.008 1.007 0.989
Go to: 
Contents
Previous
Next