EDP Sciences
Free Access
Volume 446, Number 2, February I 2006
Page(s) 747 - 771
Section Instruments, observational techniques, and data processing
DOI https://doi.org/10.1051/0004-6361:20053818
Published online 13 January 2006
A&A 446, 747-771 (2006)
DOI: 10.1051/0004-6361:20053818

Representations of spectral coordinates in FITS

E. W. Greisen1, M. R. Calabretta2, F. G. Valdes3 and S. L. Allen4

1  National Radio Astronomy Observatory, PO Box O, Socorro, NM 87801-0387, USA
    e-mail: egreisen@nrao.edu
2  Australia Telescope National Facility, PO Box 76, Epping, NSW 1710, Australia
3  National Optical Astronomy Observatories, PO Box 26732, Tucson, AZ 85719, USA
4  UCO/Lick Observatory, University of California, Santa Cruz, CA 95064, USA

(Received 12 July 2005 / Accepted 5 October 2005 )

Greisen & Calabretta (2002, A&A, 395, 1061) describe a generalized method for specifying the coordinates of FITS data samples. Following that general method, Calabretta & Greisen (2002, A&A, 395, 1077) describe detailed conventions for defining celestial coordinates as they are projected onto a two-dimensional plane. The present paper extends the discussion to the spectral coordinates of wavelength, frequency, and velocity. World coordinate functions are defined for spectral axes sampled linearly in wavelength, frequency, or velocity, linearly in the logarithm of wavelength or frequency, as projected by ideal dispersing elements, and as specified by a lookup table.

Key words: methods: data analysis -- techniques: image processing -- techniques: radial velocities -- techniques: spectroscopic -- astronomical data bases: miscellaneous

© ESO 2006

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