On 2005-Jan-24, OPUS 15.5 was installed in the Multi-mission Archive at STScI (MAST). This build includes version 2.17b of the CALSTIS code for use in the On-The-Fly-Recalibration (OTFR) pipeline for STIS data products. This makes the pipeline products more consistent with data recalibrated with version 2.17 of CALSTIS which was released as part of STSDAS version 3.3.

Features which were available in the STSDAS 3.3 release, but which are now available in OTFR for the first time include:

• The inclusion of time-dependent sensitivity changes in the calculation of the PHOTFLAM value and other imaging mode photometric keywords.
• Use of the temperature history given in the EPC file for the scaling of the CCD dark current.
• Improved treatment of echelle wavecals taken using long slits.

Version 2.17b of the CALSTIS code does contain two important fixes to errors in version 2.17:

• When doing 2D-rectification of binned CCD data, version 2.17 incorrectly scales the slit angle, leading to a small spurious rotation of the x2d or sx2 file.
• When doing a polynomial fit to the background region, CALSTIS 2.17 will crash if all background points are rejected from the fit due to geocoronal line contamination. This may happen, for example, in slitless G140L spectra.

Subsequent to the delivery of CALSTIS 2.17b for pipeline use, three additional programming errors (an undefined variable, an out-of-bounds array access, and a malformed if-statement) were identified. The latter errors do not appear to have created any problems for the MAST OTFR pipeline at STScI, but have produced intermittent run-time and processing errors on some operating systems. These errors are fixed in CALSTIS 2.18.

A patch to include these latest CALSTIS changes in users' local STSDAS installations is now available at http://www.stsci.edu/resources/software_hardware/stsdas/download. This patch will also include the corrected fringe-flat scripts discussed in the December 2004 STAN, as well as an updated version of the Multidrizzle package.

The new version of OPUS will now also apply additional calibration steps to some slitless spectroscopic observations that previously were not fully calibrated by OTFR. These additional steps include division by flat fields and extraction of a one-dimensional spectrum. Since the software cannot automatically correct for any displacement of the target in the dispersion direction, for significantly off-center targets this will result in a large error in the wavelength scale and a corresponding mis-alignment of the sensitivity function with the observed spectrum, so pipeline produced wavelength and flux extractions for slitless observations should be treated with caution.