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IRAM Memo 2011-4
Description of the spectral axis handling in CLASS
J. Pety$^{1,2}$ & S. Bardeau$^1$

1. IRAM (Grenoble)
2. LERMA, Observatoire de Paris

July 6 $^\ensuremath{\mathrm{th}}$, 2019
Version 1.2
(Version 1.1 released on October 10 $^\ensuremath{\mathrm{th}}$, 2014)
(Version 1.0 released on October 20 $^\ensuremath{\mathrm{th}}$, 2011)

Abstract:

An observer is interested by the physical properties (line frequencies, velocity of the gas) of a source in its own reference frame. However, the observations happen in a different frame, namely the topocentric frame for ground-based observations. This implies a change of frame to infer the physical properties in the source frame from the measured frequencies in the measurement frame. This memo tries to explain the different interpretation of the spectral axis, the additional subtleties related to heterodyne receivers in radio-astronomy, the current description of the spectral axis handling in CLASS, and the impact of various short-comings that happen for historical reasons.





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