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Sflats

Sflats constructs a spectroscopic flat field image for use with biasflat. Sflats does the following:

• Combine one or more flat field frames
• Remove bias
• Normalize each flat field spectrum to unity

 

USAGE	Sflats -m mapfile -f flatfile[s] [-b biasfile] [-o outputfile] [-z badpixfile]
INPUT	mapfile is the name of the mapfile which describes the data flatfile[s] is the name[s] of a spectroscopic flatfield set biasfile is the name of a bias file set , outputfile is the name of the output file if more than two input files badpixfile is the name of a non-standard bad pixel file
OUTPUT	flatfile_flat_cn.fits or outputfile_cn.fits are the processed flats
PARAMETERS	minlambda minimum wavelength maxlambda maximum wavelength telscale telescope scale arcsec/mm bias_file bias frame to use (or "none") shuffled distance, in pixels, to shuffle the spectra border width of border around spectrum fit_mode continuum fitting method (median or poly) order order of fit if polynomial fitting med_box width of sliding box if median fitting

 

Details:

Sflats first removes the bias level from each input file, using a bias frame if provided, or otherwise using the overscan areas. Multiple frames are summed. The spectral response of the flat field continuum lamp is fit in each spectrum, either by polynomial fitting or by a running median, and the fit is used to normalize each spectrum to unity. If a bad pixel file is specified, it is used to mask out regions before the spectral response is fit. Otherwise, the standard, dewar-specific bad pixel file is used.

 

The choice of continuum fitting method to use depends on the data. For long camera grating spectra, the polynomial fitting method works well. However, for short camera grism spectra, where the spectra are often contaminated by the zero order images, the median fit is much more reliable, if a bad pixel mask for the zero order image is not specified.

 

If minlambda and maxlambda are both set to 0, Sflats uses the values from the map file.

 

The output is a file or files called filename_flat. If there is only one input flat file, its name is used for filename. If there are two input file, filename is constructed from the two input file names. If there are more than two input files, filename must be specified.

 

If the observations were taken in nod&shuffle mode and the spectral flats were not themselves shuffled during the exposure, a shuffled flat frame can be produced by setting shuffled to the shuffle distance, in pixels. If however, the spectral flats are already shuffled, the shuffled parameter must be set to zero.

 

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