January 14, 2022
COS NEWSLETTERS

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In this STAN we announce the release of documentation relevant to the preparation of Cycle 30 COS proposals. We also announce a new COS data processing walkthrough notebook and the incorporation of updated dark rates into the COS exposure time calculators. 

Release of Cycle 30 Documentation

Documentation relevant to the preparation of Cycle 30 COS proposals has been released. This includes information pertaining to COS in the HST Call for Proposals and Primer as well as an updated edition of the COS Instrument Handbook. The most significant news is the introduction of Lifetime Position 6, which will become the default for G160M spectroscopy at the beginning of Cycle 30. The new documentation discusses the increased wavelength calibration overheads at LP6 and the circumstances under which G160M observations may be conducted at LP4 instead.

 

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New COS Notebook: Splitting COS TIME-TAG Exposures into Sub-Exposures with splittag

COS spectra are almost always recorded in TIME-TAG mode, in which each individual encounter with a photon is recorded with its own metadata such as the time of the encounter. With TIME-TAG data, one can split a COS exposure into multiple sub-exposures. For instance, a transit may occur during the exposure, and it may be valuable to analyze the spectrum before, during, and after the transit. The functionality to do this is built into the COSTools python module with the tool splittag.

The next entry in the COS team's series of data processing walkthrough notebooks has been released; it demonstrates how to use splittag.

 

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New Dark Rates Adopted for ETC v30.1

The dark rates for the COS FUV detector (FUVA and FUVB) and the COS NUV detector are monitored regularly. The dark rate of the FUV detector, primarily segment A, experiences occasional changes from its nominal baseline. See COS ISR 2019-11 for discussion of the variable, spatially structured component of the FUVA dark rate and recent efforts to more accurately account for it. Further details about the dark rate monitor, including links to the latest plots of the dark rates against time, may be found at the COS Monitoring page.

The FUV dark rates adopted by ETC version 30.1 have changed since the previous version. The new dark rates are 2.01E-6 counts/sec/pixel for FUVA (unchanged) and 1.84E-6 counts/sec/pixel for FUVB (up by 8%). The dark rates for Spectroscopic Target Acquisition are now 3.15E-6 counts/sec/pixel for FUVA (up by 1%) and 3.08E-6 counts/sec/pixel for FUVB (up by 9%).

The NUV dark rate adopted by ETC version 30.1 is 1.19E-3 counts/sec/pixel (down by 1%).

Additionally, the ETC has been updated with the latest throughputs for all COS modes, incorporating changes in sensitivity with time. PIs are strongly encouraged to use the latest version of the ETC for determining exposure times for use in their Phase II proposals.

 

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