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: http://www.stsci.edu/documents/dhb/web/c23_stisdataV2.fm3.html
Дата изменения: Wed Jul 1 20:35:20 1998 Дата индексирования: Sat Dec 22 16:09:02 2007 Кодировка: |
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Raw data from isolated wavecals, biases, darks, and flats, as well as from ACQs and ACQ/PEAKs, have the _raw suffix.
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20.3.1 Understanding Associations
A single FITS file will contain multiple science exposures whenever an associated set of science exposures is taken. Associations are created for target acquisitions, auto-wavecals, crsplits, and repeatobs (nexp=many in the RPS2 file). You can recognize a data file as an associated set for STIS because there will be a zero in the last position of the rootname (e.g., o3tt01010_raw.fits). The rootnames of the individual exposures in an associated data set are contained in the association file, which has suffix _asn (e.g., o3tt01010_asn.fits). An association file holds a single binary table extension, which can be displayed with the IRAF tasks tprint or tread. The information within an association table shows how the associated exposures are related. Figure 20.2 illustrates the contents of the association table for a CRSPLIT=2 observation, with an associated autowavecal.
Figure 20.2: Contents of Association Table
The association table above tells the user that the product, or data set, will have the rootname o3tt01010, that there will be two science exposures contained in the o3tt01010_raw.fits file which are CRSPLITS, and that a o3tt01010_wav.fits file should exist containing the contemporaneously obtained automatic wavecal. The o3tt01010_raw.fits file will contain six image extensions, one triplet of {SCI, ERR, DQ} for each exposure (see Figure 20.1). The pipeline will calibrate this data as a unit, producing a single cosmic ray rejected image (rootname_crj.fits) along with its data quality and error images as well as rectified spectra. Similarly, for repeatobs observations, in which many identical exposures are taken to obtain a time series, all the science data will be stored in sequential triplet extensions of a single FITS file. These will be processed through the calstis pipeline as a unit, with each image extension individually calibrated and the set of images also being combined to produce a total time-integrated, calibrated image. See Chapter 21 for more information about the pipeline processing. 