One-dimensional spectral extraction as part of the pipeline calibration has been enabled for first-order and echelle modes in calstis v1.6, which was installed in the pipeline on 2 Feb 1998.

For echelle modes, each echelle order is extracted. If an order is not found (as may occur when it is near the edge of the detector), it is skipped. Detailed parameters used for the extraction are specified in the SPTRCTAB and XTRACTAB reference files.

For first order modes, point source extraction is performed with a 1024 pixel high search range for the cross correlation routine used to locate the spectrum, so that the brightest spectrum along the slit is extracted. The location of the extracted spectrum is written into the trailer file in the pipeline calibration, or as standard output when running the stand-alone x1d iraf task.

More detailed information about first-order extraction is available in STIS ISR 97-02, available on the STIS WWW page under documentation.

Cosmic Ray Rejection (calstis2/ocrreject)

In the pipeline, sky background will now be accounted for in cosmic ray rejection. The sky background is subtracted off before cosmic ray rejection takes place, and is added back into the final output image. This capability is controlled by the crr calibration reference file (CRREJTAB) and has been enabled by setting SKYSUB to 'mode' in the new CRREJTAB used in the pipeline instead of the previous value of 'none'. A new primary header keyword, SKYSUM, has also been added that specifies the value of the sky background determined by calstis.

An additional new primary header keyword, REJ_RATE, has been added specifying the cosmic ray rejection rate determined from the co-added, cosmic ray rejected input images.

The corresponding stand-alone iraf cosmic ray rejection task (ocrreject) has also been enhanced. It now takes multiple file input, and has been made more robust by allowing various new input parameters to the task. These input parameters control the processing in a manner identical to the default parameters from the CRREJTAB. The new input parameters are:

table	specifies a non-default crrejtab reference file to be used
scale	multiplicative factor (%) applied to the noise
init	initial guess method (minimum or median)
sky	sky subtraction method (none or mode)
sigmas	sigmas used in successive crr iterations (e.g., 5,4,3)
radius	rejection propagation radius in pixels
thresh	rejection propagation threshold
pdq	data quality flag bits to reject
crmask	yes or no) update the input data quality flags for crr pixels

The verbose option now also provides more output.

The CRCORR calibration switch is now set to perform when NRPTEXP > 1, even if no cr-splitting was performed. Repeat exposures are cosmic ray rejected and summed in a manner identical to CRSPLIT exposures.

Photometric calibration for filtered imaging observations

The photometric calibration keywords (PHOTFLAM, etc.) were incorrectly populated for filtered imaging modes because the filter throughput was not being taken into account. When doing PHOTCORR in calstis1, the APERTAB is now read to get the filter throughput and it is included in the computation. This is only relevant for imaging observations. If the APERTAB keyword is missing from the header, a warning will be printed, but computation of PHOTFLAM, etc., will continue anyway.

Flux calibration for 1- and 2-d spectral extraction

FLUXCORR, the conversion to absolute flux in calstis6 (x1d), previously did not take into account the fact that a finite height extraction aperture was used when generating the throughput reference tables (PHOTTAB - _pht.fits). Beginning with calstis v1.7, the throughputs in the PHOTTAB reference file will be for an "infinite" extraction region. The factor to correct from a finite extraction region to an "infinite" region is contained in a new reference table with header keyword PCTAB, and calstis6 now applies the correction from this table to the flux conversion. Note that this correction is not applied for FLUXCORR in calstis7 (x2d), which uses the PCTAB factor only for computing the DIFF2PT keyword value.

When recalibrating data that does not contain the PCTAB keyword, the best pctab can still be identified using the starview Reference screen. A PCTAB for the data will be shown under "Recommended", even though the "Used" field is blank. [Note that currently a bug in this system says that the degree of "Severity" of the change is N/A, which is incorrect.] After retrieval of the reference file from the archive, the PCTAB keyword and name of the reference file should be added to the primary header of the science (_raw) file before recalibration.

Note that these calstis changes are accompanied by new throughput reference files ( PHOTTAB) for all detectors that incorporate the in-flight calibration for first order modes. Anyone with first order mode data taken prior to installation of calstis v1.7 in the pipeline is strongly advised to recalibrate their data to get a more accurate flux calibration.

Stand-alone iraf tasks now take wildcard input

The stand-alone iraf calibration tasks (calstis, basic2d, x1d, x2d, ocrreject, wavecal) now take wildcard file name input. The standard IRAF notation for wildcards of image names is supported, including * and @list. For example:

  calstis *_raw.fits
  basic2d  *_raw.fits  *%_raw%_flt%.fits
  basic2d *_raw.fits ""
  basic2d  abc1.fits,abc2.fits,abc3.fits  
           xyz1.fits,xyz2.fits,xyz3.fits
  basic2d  @in  @out

Calibration reference files/recalibration

To solve some problems associated with identification of the best reference files for recalibration, combined with the fact that when using the starview Reference screen to retrieve the latest reference files only the science portion of an associated data set is used in the screen, calstis now compares reference file names in the science header and wavecal header. If there are any differences, a warning is printed, and the file name from the science header is used for calibrating both files. This means that if reference files are updated in the science file using the recommended files from the starview Reference screen interface, these updated files will also automatically be used in calibrating the wavecal observation. There are two exceptions, LAMPTAB and BIASFILE. LAMPTAB may be absent or blank in the science file header, in which case the file from the wavecal header is used. Because the wavecal bias file can have different binning than the science file, the WBIAFILE keyword in the science header (if the keyword is present) is compared with BIASFILE keyword in the wavecal header, and WBIAFILE takes precedence. If the binning and gain of the two files are the same, then the BIASFILE values are also compared.

There are some reference files for calstis that are optional, in the sense that the keyword may be missing, blank, or "N/A", in which case calstis continues processing but the correction will not be applied. Currently there are two such files, APERTAB for PHOTCORR in calstis1 and PCTAB for FLUXCORR in calstis7. However, if the keyword has a value other than blank or "N/A" and that file does not exist, calstis stops processing and prints an error message.

Summing multiple exposure echelle obseravtions

If an observer had repeat exposure echelle observations and had set RPTCORR and X2DCORR to PERFORM, calstis would previously crash and not sum the repeated exposures properly. (Note that X2DCORR is not set to perform in the pipeline calibration for echelle observations, so this problem would have only been relevant for users who were attempting to run calstis or x2d outside the pipeline.) This problem has now been corrected, and imsets corresponding to the same spectral order are now summed and output in an _sx2 file.

A number of additional enhancements and minor problem fixes include:

• The "good time interval" (GTI) extension tables for some timetag data files (_tag.fits) had incorrect good time intervals in the table. This problem has been corrected.
• When doing bias level subtraction (BLEVCORR), the virtual overscan region is now used to determine the variation along the first image axis.
• Dark correction in calstis1 was modified to sum pixel values instead of averaging, in the case that the dark reference image needs to be binned down to match the uncalibrated image.
• The file name for the output 1-D extracted data had suffix _sx1 even in the case that the raw data were in just one imset. The suffix in this case should have been _x1d.
• When a first-order grating was used, calstis6 and calstis7 no longer try to check that the spectrum is within the input image.
• 2-d rectification (calstis7) was modified so that it reduces the size of the output image if the input image is a subarray.
• The POSTARGn keywords in wavecal files (_wav.fits) often contained spurious values.
• The flux values in ACQ/PEAK images for very bright sources were incorrect.
• The NRPTEXP keyword was being populated incorrectly (it was too large by 1) for all associated, repeat exposure datafiles (such observations can be identified by their value of ASN_MTYP = REPEATOBS in the association (_asn) table for an associated dataset).
• The SMALL_NSIGMA cosmic ray rejection parameter in wavecal processing (calstis4) was set to 1. For some images this was too small, as it resulted in many good pixels being rejected as cosmic rays in a portion of the image that is actually illuminated but was incorrectly flagged as being behind an occulting bar due to an offset, e.g. of the Mode Select Mechanism. The value has been changed to 2.
• In 2-d spectral extraction (calstis7/x2d) calstis was writing the CRVAL1 and CD1_1 keywords in units of angstroms instead of the default FITS-standard of meters. One of the ill consequences of this was that iraf plotting tasks such as splot labelled the wavelength scale in meters when the actual wavelength values were in angstroms. To rectify this problem, the CUNIT1 keyword is now also written to the extension headers with a value of "angstrom."
• the echplot iraf task has been enhanced to make it more user-friendly and the output plots more useful