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prepspec stis



prepspec -- Prepare STIS G750L or G750M spectrum for subsequent de-fringing procedures


prepspec inspec


Input (2-D) spectral image to be corrected for fringing
(outroot = "")
Root for output file name. If this value is null (the default), the output file names will be constructed from the input name. If outroot ends in "/" it will be interpreted as a directory, and the input file name will be appended and used as the basis of the output file names. Otherwise, the output file names will be constructed by appending such strings as "_crj.fits" to outroot (or if outroot ends in "_raw.fits", that string will be replaced by "_crj.fits", etc.).
(darkfile = "")
Name of (reference) superdark image to be used for dark subtraction. If this value is null (the default), the DARKFILE keyword in the main header of inspec will be used (in that case, make sure it is correctly populated)
(pixelflat = "")
Name of reference flat field image to perform pixel-to-pixel correction
(initgues = "min")
Initial value estimate for cosmic ray rejection (min|med)


PREPSPEC prepares STIS G750L or G750M spectra for subsequent fringe correction procedures (tasks mkfringeflat and defringe ). PREPSPEC is intended only for STIS first-order CCD spectra at wavelengths longer than about 700 nm, which suffer from fringing.

The input 2-D spectral image inspec [typically a STIS fits file with "_raw" file suffix, but any file name is allowed] is first run through the STIS pipeline calstis in order to perform bias subtraction, cosmic ray rejection, dark subtraction, and division by a pixel-to-pixel flat field. In case of G750M data, wavelength calibration and 2-D rectification is performed as well. An appropriate superdark file can be provided as parameter darkfile , as can a pixel-to-pixel flat field. If these reference files are not specified, the ones listed in the image header will be used. The initial value estimate during cosmic ray rejection can be specified by means of parameter initgues . The possible entries are min (minimum; the default) and med (median). The log file of the calstis reduction steps is written to output file prepspec.log .


The input STIS spectral image inspec must be a (STIS-standard) "multi-imset" FITS file, with three extensions (or groups) per imset: science (EXTNAME=SCI), error (ERR), and data quality (DQ). PREPSPEC will read each imset, calibrate it, and produce a multi-group output FITS file.

The output spectrum is a single-imset STIS FITS file with three extensions. The output spectrum must be used as input spectrum to tasks mkfringeflat (which optimizes the fringe flat field) and defringe (which performs the final fringe correction).


1. Prepare STIS spectrum for subsequent fringe correction procedures. Use superdark file "mysuperdark.fits" to provide the most up-to-date correction of hot pixels.

    cl> prepspec o3st20gdr_raw.fits darkfile="mysuperdark.fits"

2. Example of all steps involved in fringe correction for a G750M spectrum o3st20gdr_raw.fits and its associated contemporaneous fringe flat o3st20gds_raw.fits:

    cl> normspflat o3st20gds_raw.fits normff750M.fits \
    >>> darkfile="mysuperdark.fits" wavecal="o3st20gdr_wav.fits"
    cl> prepspec o3st20gdr_raw.fits darkfile="mysuperdark.fits"
    cl> mkfringeflat o3st20gdr_sx2.fits normff750M.fits normff750M_fin.fits
    cl> defringe o3st20gdr_sx2.fits normff750M_fin.fits \
    >>> outspec="o3st20gdr_final.fits" do_cal-

3. Same as 2, but for a G750L spectrum o3st20gda_raw.fits, wavecal o3st20gda_wav.fits and contemporaneous fringe flat o3st20gdb_raw.fits:

    cl> normspflat o3st20gdb_raw.fits normff750L.fits \
    >>> darkfile="mysuperdark.fits" wavecal="o3st20gda_wav.fits"
    cl> prepspec o3st20gda_raw.fits darkfile="mysuperdark.fits"
    cl> mkfringeflat o3st20gda_crj.fits normff750L.fits normff750L_fin.fits
    cl> defringe o3st20gda_crj.fits normff750L_fin.fits \
    >>> outspec="o3st20gda_defr.fits" do_cal-



Task created by Paul Goudfrooij on April 20, 1998.
Task modified by Paul Barrett on October 21, 2004.



calstis, normspflat, mkfringeflat, defringe

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