class Continuum and Line Analysis Single-dish Software - IRAM

4.4. CLASS FITS FORMAT 43
more elaborate projection systems. In the current example, the position really observed is
Dec = CRVAL3 + ( 1 - CRPIX3 ) * CDELT3
Ra = CRVAL2 + ( 1 - CRPIX2 ) * CDELT2 / COS(Dec)
That is, CDELT2 and CDELT3 represents angular offsets from the reference position
(CRVAL2,CRVAL3) in a Global Sinusoidal projection (RADIO projection).
7. Stokes parameters as defined in the basic paper of Wells et al.
8. Galactic latitude and longitude of the reference position, i.e. of the position
(CRVAL2,CRVAL3). If one was using galactic coordinates instead of equatorial ones, the
RA and DEC would appear here instead.
9. Epoch of these coordinates.
10. Molecular line name, for bookkeeping.
11. Rest frequency.
12. LSR Velocity of the reference channel. Heliocentric velocities can be used also.
13. Velocity spacings of the channels. This information is duplicate with the rest frequency
and frequency spacing of channels, but convenient. The velocity of a given channel is thus
given by
V(i) = VLSR + ( i - CRPIX1 ) * DELTAV
14. Image frequency, for double sideband operation.
15. System temperature, necessary for some kind of weighting when adding a number of spectra.
16. Integration time, used for the same reason as above.
17. Scan number, for bookkeeping.
18. Atmospheric opacity in the signal sideband.
19. For multi-phased spectra (i.e. frequency switching) number of phases.
20. For each phase, the frequency offset, the phase length and weight.
21. The telescope beam efficiency.
22. The telescope forward efficiency.
23. The ratio of gains in the image and signal sidebands (in case of double sideband operation).
24. Some “History” comments. Whether this information should be given with specific keywords
or in an History record is still an open question. This information is not really needed
for further data reduction, but it helps bookkeeping.
25. The list of scan numbers of the spectra added to produce this one.
The FITS interface for Continuum data is still experimental. Try it, and send your comments...