October 8, 2021

# October 2021 STAN

In this STAN we announce the delivery of a new version of the Image Photometry Table (IMPHTTAB) for STIS and the end of HSTCAL support for RHEL 6.

### New Image Photometry Table (IMPHTTAB) Delivered for STIS

On September 21, 2021 the STIS team delivered an updated version of the Image Photometry Table (IMPHTTAB; 59l1632po_imp.fits) to the HST Calibration Reference Data System (CRDS) for use with post-Servicing Mission 4 (SM4; in 2009) observations. The IMPHTTAB reference file is used by the IRAF-independent CALSTIS pipeline to determine the photometric parameters (PHOTFLAM, PHOTBW, and PHOTPLAM) for the STIS imaging modes across all three detectors (FUV, NUV, and CCD). This file contains inverse sensitivities informed by the spectral time dependent trends, reference magnitudes, pivot wavelengths, and root-mean squared (RMS) bandwidths.

The previous version of IMPHTTAB (y2i1649no_imp.fits) was delivered in February 2014. For observations taken after this date, CALSTIS would extrapolate the photometric parameter values assuming the same time dependent trends from 2014. Comparing the IMPHTTAB extrapolations from the previous reference file to current calculations from PySynphot, the STIS Team found mean differences in the PHOTFLAM values of ~4%, with a maximum difference of 48% for the FUV-MAMA/MIRROR/0.2X29 mode.

With the newly delivered IMPHTTAB, our verification process showed that the differences between the photometric parameters estimated with PySynphot and those by CALSTIS are reduced to < 1% for all modes. This latest version of the reference file will improve the accuracy of the flux calibration of the STIS imaging modes, particularly for observations taken after 2017. All STIS imaging data has now been reprocessed with the new IMPHTTAB file and is available from the HST archive. We advise users who require the best flux calibration to re-retrieve their observations and check IMPHTTAB = 59l1632po_imp.fits in the image headers to verify the version. For any questions regarding the updates to the IMPHTTAB reference file, please contact the HST help desk.

### End of Support for Red Hat Enterprise Linux 6 in HSTCAL

The HSTCAL package no longer includes a distribution for Red Hat Enterprise Linux (RHEL) 6, beginning with the HSTDP-2021.3.3 (HST 2.7.2, CALDP_20210721_CAL_final) build. The version of RHEL on a system can be determined with the command cat /etc/redhat-release. Support for RHEL 6 updates (including security patches) was dropped by Red Hat in November 2020. Currently installed conda environments will continue to work on RHEL 6 systems; only HSTCAL distributions starting with CALDP_20210721_CAL_final will not be created successfully. We caution against trying to update currently working environments, which could result in a corrupted environment due to inconsistencies between packages. We expect this change to affect only a small number of external users. Users experiencing problems installing the latest stistools (version 1.3.0) due to this issue should contact the HST help desk.