CALNIC A & B

  As already mentioned in section 2.6.2 CALNIC C expects a pair of calibrated direct and grism images as input.

There are two steps in the calibration pipeline for NICMOS:

• the first one, CALNIC A, is meant to remove instrumental signature from each given raw exposure;
• the second one, CALNIC B, has been introduced in the pipeline with the advent of the concept of associations in the data-handling of the new instruments, NICMOS and STIS. From all the exposures in the association it builds the final product.

The idea beyond an association is that an observer, in order to improve flat-fielding or to remove cosmic rays or to subtract the thermal background, can ask for multiple exposures for a given target; these exposures are logically grouped and used together to obtain a single final product.

Therefore CALNIC B, getting as input the FITS association file (provided by the stsdas pipeline) builds the final product from all the calibrated exposures part of that association.

Both CALNIC A and CALNIC B are written in ANSI C. Data I/O is accomplished using IRAF I/O library functions. A set of C to IRAF interface routines (developed at STScI) provides the link between the calibration software and the IRAF libraries. Therefore `calnica' and `calnicb' are stand-alone programs which can be run at the unix prompt level:

% cd $SOURCE_DIR (where the input files have been retrieved)
% calnica input_raw [output_cal]

where input_raw is the filename of a raw exposure; the default output filename is the dataset name"_cal.fits". E.g.,

% calnica n3s2150ao_raw.fits

will produced a calibrated exposure called n3s2150ao_cal.fits

% calnicb asn_id

where asn_id is the association identifier to which corresponds an association binary fits table called asn_id."_asn.fits". E.g.,

% calnicb n3s215040

will read the n3s215040_asn.fits association table and produce the final product n3s215040.fits -and all the other intermediate products.