Computer Science
Scientific paper
Jul 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010hstc.worke..70t&link_type=abstract
"2010 Space Telescope Science Institute Calibration Workshop - Hubble after SM4. Preparing JWST, held 21-23 July 2010 at Space T
Computer Science
Scientific paper
The A-to-D conversion, or gain, of the NICMOS detectors depends on a combination of detector temperature and bias voltage. The response of the three NICMOS detectors changed slightly due to changes in the A-to-D conversion over both the era before the installation of the NICMOS Cooling System (NCS) 1997-1998 and after the installation 2002 -2008. This change can been expressed as a change in an effective temperature (or equivalently A-to-D conversion) referred to as biastemp, which is calculated directly from the bias level of the science exposures. Here we discuss the creation of new flat-field reference files used to correct for changes in the structure of flat-fields caused by the change in A-to-D conversion. These reference files (* tdf.fits) populate the keyword TDFFILE in the headers of pre-NCS data retrieved from the OTFR after January 23, 2009 and post-NCS data retrieved after November 19, 2008 and are used by the FLATCORR step in calnica version 4.4 and later. Each * tdf.fits file consists of five different extensions each valid at a different biastemp range. During calibration, the pipeline calculates the biastemp of the science image and then uses the flat-field extension with the best matching biastemp. For consistency check we also created epoch dependent flat-fields for post- NCS data and compared them with the biastemp dependent flat-fields.
Dahlen Tomas
Thatte Deepashri
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