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.

LogS=A+B×Logν+C×(Logν)2+D×(Logν)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

Connect with NRAO

The NSF National Radio Astronomy Observatory and NSF Green Bank Observatory are facilities of the U.S. National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Founded in 1956, the NSF NRAO provides state-of-the-art radio telescope facilities for use by the international scientific community. NSF NRAO telescopes are open to all astronomers regardless of institutional or national affiliation. Observing time on NSF NRAO telescopes is available on a competitive basis to qualified scientists after evaluation of research proposals on the basis of scientific merit, the capability of the instruments to do the work, and the availability of the telescope during the requested time. NSF NRAO also provides both formal and informal programs in education and public outreach for teachers, students, the general public, and the media.

The U.S. National Science Foundation (U.S. NSF) is an independent federal agency created by Congress in 1950 "to promote the progress of science; to advance the national health, prosperity, and welfare; to secure the national defense..."

AUI collaborates with the scientific community and research sponsors to plan, build, and operate cutting-edge facilities. We cultivate excellence, deliver value, enhance education, and engage the public.