COMICS FITS information

Data structure

Odd numbers are assigned to imaging data (for imaging observations or slit-viewer images for spectroscopy), while even numbers are reserved for the spectrograph (i.e., they contain no data and only the FITS headers for imaging observations and spectra for spectroscopy).

COMA FITS files: raw data

COMICS FITS files are 4-dimensional: X × Y × Z × W

X X-axis (320 pixels)
Y Y-axis (normally 240 pixels)
Z time sequence of data (beamA, chop to beamB, chop back to beamA, etc.)
W detectors (COMICS has 6 detectors but ignore this dimension for imaging as only one is used)

COMA files consist of a series of A1,B1,A2,B2,A3,B3,...i.e., (co-added) images taken at each chop position (in each beam) in turn. In one of the examples provided below (COMA00102607.fits), there are 11 images each taken at each chop position (beamA or beamB) and so there are 22 images in total. At mid-infrared wavelengths, sky is usually much brighter than an object and each of these images will probably not show anything. That is why we employ the chopping technique and what we should now do is subtract the beamB image from each preceding beamA frame.

i.e., (A1-B1), (A2-B2), (A3-B3), etc.

COMA files are provided for more thorough/rigorous data reduction/analysis.

Sample FITS files

Imaging Spectroscopy
COMA00102607.fits[320,240,22,1][int]: HD20644 COMA00102591.fits[320,240,24,1][int]: HD20644
COMA00102608.fits[320,240][int]: HD20644 COMA00102592.fits[320,240,24,2][int]: HD20644

Sample FITS headers

Imaging Spectroscopy
COMA00102607.txt[320,240,22,1][int]: HD20644 COMA00102591.txt[320,240,24,1][int]: HD20644
COMA00102608.txt[320,240][int]: HD20644 COMA00102592.txt[320,240,24,2][int]: HD20644

COMQ FITS files: quick-look data

COMQ files contain the results of a quick background subtraction,

i.e., (A1-B1) + (A2-B2) + (A3-B3) + ...

This is what is displayed on the quick-look viewer at the summit during observations.

Sample FITS files

Imaging Spectroscopy
COMQ00102607.fits[320,240,1,1][int]: HD20644 COMQ00102591.fits[320,240,1,1][int]: HD20644
COMQ00102608.fits[320,240,1][int]: HD20644 COMQ00102592.fits[320,240,1,2][int]: HD20644

Note that the third dimension of each of the above FITS files is now 1.

Sample FITS headers

Imaging Spectroscopy
COMQ00102607.txt[320,240,1,1][int]: HD20644 COMQ00102591.txt[320,240,1,1][int]: HD20644
COMQ00102608.txt[320,240,1][int]: HD20644 COMQ00102592.txt[320,240,1,2][int]: HD20644

COMICS specific FITS header keyword dictionary


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