16.2 NICMOS Calibration Software

1. calnica: This routine removes the instrumental signature from the science data. It is the first calibration step, and is applied to all NICMOS datasets individually. Calnica operates on the raw science data files.
2. calnicb: This routine operates on associations: it co-adds datasets obtained from multiple iterations of the same exposure, mosaics images obtained from dither patterns, and background-subtracts images obtained from chop patterns. Calnicb is applied to the calibrated science data files (output from calnica), and requires association tables and the *_spt.fits files. Both tasks determine which calibration steps are to be performed by looking at the values of the calibration switches keywords in the primary header of the input science data files (see Table 15.5). The tasks select the reference files to use in the calibration of the data by retrieving the reference file names from the reference file keywords. The appropriate values of the calibration switches and reference file keywords depend on the instrumental configuration used, the date when the observations were taken, and any special pre-specified constraints. They are set in the headers of the raw data file in the pipeline during the generic conversion process. The calibration indicators keywords record which steps have been performed on the data, and get updated after processing. In particular, the indicators for completed steps will have been assigned the value "PERFORMED", while the indicators for the steps that were not performed will have been set to "OMITTED" or "SKIPPED". The calibration indicators keywords should be examined in the primary header of the calibrated science data (*_cal.fits) to determine what calibration steps were applied to the data.

   The calnica and calnicb tasks are available in STSDAS under the hst_calib$nicmos package. By using these tasks, observers can recalibrate data using the same software as the routine calibration pipeline at STScI.

Calnicc was developed using the Interactive Data Language (IDL) software at the Space Telescope European Coordinating Facility (ST-ECF). Currently calnicc is not part of the automatic pipeline processing, and users must apply the calibration software to their grism images. The manual (written by W. Freudling and R. Thomas) describing the software, its installation, and use can be found at the following WWW address:

http://ecf.hq.eso.org/nicmos/calnicc/calnicc.html

http://ecf.hq.eso.org/nicmos/nicmoslook