Journal Article

Radio source calibration for the Very Small Array and other cosmic microwave background instruments at around 30 GHz

Yaser A. Hafez, Rod D. Davies, Richard J. Davis, Clive Dickinson, Elia S. Battistelli, Francisco Blanco, Kieran Cleary, Thomas Franzen, Ricardo Genova-Santos, Keith Grainge, Michael P. Hobson, Michael E. Jones, Katy Lancaster, Anthony N. Lasenby, Carmen P. Padilla-Torres, José Alberto Rubiño-Martin, Rafael Rebolo, Richard D. E. Saunders, Paul F. Scott, Angela C. Taylor, David Titterington, Marco Tucci and Robert A. Watson

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 388, issue 4, pages 1775-1786
Published in print August 2008 | ISSN: 0035-8711
Published online August 2008 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.13515.x
Radio source calibration for the Very Small Array and other cosmic microwave background instruments at around 30 GHz

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Accurate calibration of data is essential for the current generation of cosmic microwave background (CMB) experiments. Using data from the Very Small Array (VSA), we describe procedures which will lead to an accuracy of 1 per cent or better for experiments such as the VSA and CBI. Particular attention is paid to the stability of the receiver systems, the quality of the site and frequent observations of reference sources. At 30 GHz the careful correction for atmospheric emission and absorption is shown to be essential for achieving 1 per cent precision.

The sources for which a 1 per cent relative flux density calibration was achieved included Cas A, Cyg A, Tau A and NGC 7027 and the planets Venus, Jupiter and Saturn. A flux density, or brightness temperature in the case of the planets, was derived at 33 GHz relative to Jupiter which was adopted as the fundamental calibrator. A spectral index at ∼30 GHz is given for each.

Cas A, Tau A, NGC 7027 and Venus were examined for variability. Cas A was found to be decreasing at 0.394 ± 0.019 per cent yr−1 over the period 2001 March to 2004 August. In the same period Tau A was decreasing at 0.22 ± 0.07 per cent yr−1. A survey of the published data showed that the planetary nebula NGC 7027 decreased at 0.16 ± 0.04 per cent yr−1 over the period 1967–2003. Venus showed an insignificant (1.5 ± 1.3 per cent) variation with Venusian illumination. The integrated polarization of Tau A at 33 GHz was found to be 7.8 ± 0.6 per cent at position angle =148°± 3°.

Keywords: methods: observational; techniques: interferometric; cosmic microwave background; cosmology: observations; radio continuum: ISM; radio continuum: Solar system

Journal Article.  8774 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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