We have taken the opportunity to implement an improved treatment for the dispersion solutions for the STIS echelle settings in the latest release of the calstis pipeline. The improved code now takes the effects of the monthly offsets into account, and this results in improved wavelength accuracy.

Due to the monthly MSM motion, spectral features at opposite ends of an echelle image can move up to three low resolution pixels, with features near the top of the detector moving in the opposite sense to those at the bottom. These wavelength-dependent effects are now handled in the calibration software in conjunction with coefficients stored in expanded versions of the NUV-MAMA and FUV-MAMA dispersion (dsp) tables.

This modification to the dispersion solution is available in CALSTIS version 2.11, which has been released with STSDAS V5.11. Users can take advantage of the improved calibration by retrieving their data via on-the-fly recalibration (OTFR).