OLD VLA Calibrator Manual

The version of the VLA Calibrator Manual presented here is very much out-dated. The latest version can be found at the NRAO web pages. This version contains 5523 entries for a total of 1860 sources.

You can now search the Calibrator Manual around a region of interest.

Flux density measurements of VLA calibrators going back to December 1996 are available in the VLA calibrator flux history database. See what your favorite calibrator has been up to before you plan your next observing run. To properly interpret what you discover read this short document describing current limitations and how to use this utility.


New VLA On-Line Calibrator Tool (Requires Java). Your one-stop shopping location for finding information about VLA and VLBA calibrators. This includes plots of calibrator spectra and light curves, and in some cases visibility plots and images. This new tool is still under development so expect some delays and possibly glitches. Please send comments to caltool@nrao.edu.


Contents

Chapter 1. About the 2003 calibrator manual
Chapter 2. Flux Density Calibration
2.1 The Flux Density Scale used at the VLA
2.2 Monitoring of Flux Density Calibrators
2.3 Accurate Flux Density Bootstrapping
Chapter 3. Phase, Gain, Position and Polarization Calibration
3.1 Hints and Strategies for Successful Phase Calibration
3.2 Coordinate Systems at the VLA
3.3 Planning for good Polarization Calibration
Chapter 4. VLA Calibrators
4.1 The Key to the Calibrator Manual
4.2 The List of Calibrators (720kB)
Appendix A. High-Frequency (22 or 43 GHz) Data reduction at the VLA -- AIPS Cookbook Appendix D
Appendix B. Low-Frequency (74 or 330 MHz) Data reduction at the VLA -- Kassim & Perley
Appendix C. Hot List of Calibrators Needing Re-observation
The VLA Calibrator Manual is also available in postscript format (378kB). A plain text version (without links to figures) can be found in this ftp site under the name csource.mas. Finally, a gzipped copy of the plain text version is available (75kB).

We are working towards combining the VLA and VLBA calibrator databases and providing new and better tools to access the joint database. The plan is to design a much-improved calibrator finding tool that will also work for the EVLA and ALMA telescopes. Take a look at our calibrator specifications page. Please send any comments to gtaylor@nrao.edu.

We have begun a VLA polarization monitoring program for ~10 compact calibrators, primarily to enable better calibration of the VLBA. Each source is observed about once a month and reduced semi-automatically. The preliminary results are described in the VLA/VLBA Calibration Page.

Positions for 950 sources were refined on Aug. 28 2001 using the VLBA Calibrator Survey observations as reduced by the NASA Goddard Space Flight Center Geodesy group with the Calc/Solve package. These positions have typical positional errors less than 1 milliarcsec (see Johnston et al 1995, AJ 110, 880; and Beasley et al. in prep). This database is also the primary source of positions for the VLBA correlator. Two sources, J0259+425 and J2307+148 thought to have positions good to less than 50 mas, were discovered to be in error by more than 200 mas.

A tutorial for new users of the 74 and 330 MHz systems at the VLA has been written up by Namir Kassim & Rick Perley. It is available from http://rsd-www.nrl.navy.mil/7213/lazio/tutorial.

The Iridium constellation of satellites has begun transmitting almost continuously at 1622 MHz. This has serious consequences for 1612 MHz OH observations at the VLA, and also for continuum observations near 1622 MHz. For instructions on how to invoke a special set of front end filters to mitigate RFI see this Guide to the 18cm Front End Filters. For more details about the interaction of the VLA with the Iridium see this notice on calibration in the presence of the Iridium constellation for more details.

The flux densities calculated by SETJY for 3C286 using the coefficients determined in 1990 were systematically in error by 0.7 -- 1.7% in AIPS versions up to and including 15JAN96. See the SETJY bug notice for more details. The overall description of the flux density calibration scheme used at the VLA is described in Chapter 2.

Other useful places to look:

The JVAS catalog currently includes a list of 2118 compact radio sources in the northern sky (above 0 degrees declination, and with |b|>2.5 degrees). These have all been observed at 8.4 GHz with the VLA in A configuration. Position errors currently range from 12 - 55 mas, but see the entry on the VLBA calibrator survey below. Work is also in progress to extend the sample to -30 degrees declination.
The VLBA Calibrator Survey is an ongoing project to provide phase-reference calibrators for VLBA experiments. When completed it will contain astrometric (~1 mas) positions and 2.7/8 GHz images of the ~3000 sources in the JVAS catalog.
The VSOP 5 GHz Continuum Survey The Pre-launch VLBA observations comprise 374 strong flat-spectrum radio sources north of declination -44 imaged with the VLBA in June 1996. The site contains VLBA images at ~2 mas resolution and accurate positions for a good number of VLA and VLBA calibrators.
The Radio Optical Reference Frame at USNO. This site contains VLBI images and very accurate coordinates for over 400 sources including a number of good VLA and VLBA calibrators.
The CJPR VLBI source archive at Caltech. This site contains images of over 300 VLBI sources at declinations > 35 degrees observed in the Pearson-Readhead and Caltech-Jodrell Bank surveys. Many of these sources are excellent calibrators for the VLA and VLBA.
The VLBA 2 cm survey by Kellermann, Zensus, Vermeulen and Cohen. This site contains images of 132 sources obtained in 1 hour snapshots during multiple epochs. Many of these sources are excellent calibrators for the VLA and VLBA.


Comments? Send them to gtaylor@aoc.nrao.edu

Last Modified on 2003 April 4

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