September 2021 STAN
In this STAN we announce FUV lifetime position changes, the release of CalCOS v3.3.11, the delivery of new reference files, a new version of the COS Data Handbook, and the end of HSTCAL support for RHEL 6.
Multiple Lifetime Positions for FUV Spectroscopy in Cycle 29
Every few years, the location where spectra fall on the COS FUV detector is changed. This is one strategy to reduce the effects of gain sag, where the ability of a given location on the detector to record photons diminishes with repeated exposure to light. With past changes in lifetime position (LP), nearly all FUV settings have moved from the previous LP to the new one. Beginning in Cycle 29, in contrast, nearly every LP will host a subset of the settings, including a newly introduced LP5 for spectroscopy with cenwaves 1291 through 1327 of the G130M grating. Spectroscopy with the G140L grating will return to LP3, and other modes will remain at their Cycle 28 LPs. Consistent with the COS2025 policies, there will continue to be restrictions on the use of detector segment B at LP5. Please see the July 2021 STAN article on this topic for more details and a helpful figure.
Release of CalCOS Version 3.3.11
On September 3, 2021, a new version of CalCOS, version 3.3.11 was released. This version corrects a bug introduced in CalCOS version 3.3.10 where uncertainties for background-limited sources observed in the NUV were severely underestimated in the x1dsum files. This update has minimal differences in the absolute values in the error column from CalCOS 3.3.10 in all other FUV and NUV x1dsum files. There are no changes in the error column in the x1d files. Due to these changes, all COS users, especially those with background-limited NUV spectra, are encouraged to re-retrieve their data from MAST. CalCOS version 3.3.11 can be installed in an anaconda environment from the environment file at the astroconda GitHub.
Delivery of New Reference Files
In July 2021, an updated NUV BPIXTAB (bad pixel table), which identifies rectangular regions on the detectors that are known to be less than optimal, was delivered. The Data Quality (DQ) value definitions were changed to be consistent with those made in 2014 to the FUV BPIXTAB, which changed DQ=2 (previously a detector flaw) to DQ=1024 (low response region). A list of all DQ flags can be found in Table 2.19 of the COS Data Handbook.
Also delivered was a new FUV BPIXTAB reference file to flag new low (DQ=1024) and very low (DQ=16) response regions in the LP5 area of the detector and to remove or resize existing regions. The new file adds 11 new low response regions and removes 3 regions. None of the new low response regions are very low response regions, i.e., bad enough to warrant exclusion from the final spectra via the SDQFLAGS keyword.
Finally, for the benefit of a small number of calibration programs observed before October 2, 2017, two new LP4 FLUXTABs were delivered to correctly match zero points found within two TDSTABs (time-dependent sensitivity tables) that are currently in use.
See Section 3.7 of the COS Data Handbook for more details about the contents of all reference files. COS users are encouraged to re-retrieve their NUV data from MAST, as well as data from any programs of interest listed under "Lifetime Position 4 Enabling Programs" on the COS calibration page.
Release of Version 5 of the COS Data Handbook
Version 5 of the COS Data Handbook has been published. Major changes include documentation of new uncertainty calculations and file formats implemented in CalCOS, discussion of the new lifetime position LP5, and references to the new Jupyter Notebooks that introduce users to common procedures for working with COS data products.
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 CalCOS version 3.3.11 due to this issue should contact the HST help desk.