A new version of CALSTIS (version 2.0) has been released and is now used in the pipeline (effective November 10, 1998). This update is available for downloading from the STSDAS Advisories page.
Changes that have been made to CALSTIS in version 2.0 include:
HITM lamp wavecals now obtained with external shutter closed (CALSTIS11)
When a wavecal exposure is taken with the hole-in-the-mirror (HITM) system and the CCD detector, the current situation is that the external shutter is open. This means that the detector is exposed to the external target as well as the line lamp. During wavecal processing, CALSTIS therefore subtracts the science image from the wavecal image (after scaling by the ratio of exposure times) before the wavecal is used to determine the image shift on the detector. After November 9, 1998, the shutter will always be closed for wavecals, so CALSTIS has been revised to not subtract the science image for data obtained after this date.
Copy header information from all extensions to tables (CALSTIS6)
CALSTIS6 (x1d) reads an input file containing images, and it writes an output file containing one or more tables. CALSTIS6 copies the primary header of the input file to output, and it copies the first SCI extension header of the input file to the header of the first extension in the output file. When run on an input file that contains multiple imsets, the output file will contain as many tables as there are input imsets, but the headers, other than the first SCI header, from the input imsets are not copied to the output tables. CALSTIS6 will now copy all extension header information (which includes unique items like the exposure start time) to the x1d file.
Subtract sky only for imaging data (CALSTIS2)
During cosmic ray rejection, CALSTIS2 determines the total sky background for each image, subtracts that background before looking for outliers, then adds the background back in when summing all the images. This is appropriate for imaging data because the sky level can change from one exposure to another due to varying contributions from atmospheric emission. For spectroscopic observations, however, the emission from the atmosphere is confined to narrow emission lines; in this case subtracting the background would interfere with determination of the standard deviation of the data. CALSTIS2 no longer subtracts the sky for spectroscopic data before looking for outliers; the sky is subtracted when 1-d extraction is performed.
Doppler mode losing flux (CALSTIS1)
When on-board Doppler correction is performed by STIS, the left and right edges have less sensitivity than interior regions due to an "effective subarray". Any photon that hits the detector outside this region is ignored by the flight software, even if the photon's location would have been shifted inside the effective subarray by the on-board Doppler shift. CALSTIS1 now corrects for this problem. See ISR STIS 98-05 for further details.
Revise determination of STIS PLATESC keyword for MAMA data processed though LORSCORR (CALSTIS1)
The PLATESC listed in the header for MAMA observations is the HIGH-RES value (since that is how the data is obtained). When processed through LORSCORR, the plate scale is changed (it is doubled), but the keyword is not updated accordingly. This results in an incorrect value for the PLATESC in the processed data products. All MAMA observations that have been run through LORSCORR will have the PLATESC keyword updated.
NUV dark now scaled by temperature
CALSTIS1 now scales the NUV dark image by a factor that depends on the temperature of the NUV-MAMA charge amplifier as given by the parameter "OM2CAT" using the relation given in the STIS Instrument Handbook. This is an improvement over simply scaling by integration time, but is still not ideal. Ways to improve the dark subtraction further are still being investigated.
A number of additional enhancements and minor problem fixes include:
o The pipeline now bypasses bias correction for wavecals where the reference file is binned and the wavecal is not.
o The pipeline now masks off a smaller region around the occulting bars and off the edges of the small slits. This prevents loss of useful data if the offset in the cross-dispersion direction was not determined very accurately, a situation especially significant for the short echelle slits.
New/updated tools released with CALSTIS version 2.0 include:
ECHPLOT (upgrade): The task will now accept a null ("") for the output IGI script name, which triggers a "view only" mode. The tool will also allow for the specification of selected orders to be plotted (instead of having to plot the complete spectrum).
SDQFLAGS (new): This tool allows users to set the sdqflags keyword by selecting which types of conditions (e.g. hot pixel, saturated pixel, etc.) should cause the data to be unacceptable. The tool will convert the English descriptions to the correct number and update the header.
OVAC2AIR (new): This tool (similar to the FOS/GHRS tool vac2air) converts the wavelengths in the WAVELENGTH column of 1-D extracted STIS spectra from vacuum to air. Only wavelengths longer than 2000 Angstroms will be converted; shorter wavelengths will not be modified.