January 12, 2021

About This Article

In this STAN we announce COS posters at the January 2021 meeting of the American Astronomical Society and the incorporation of updated dark rates into the COS exposure time calculators. 

COS Posters at AAS 237

Two COS posters are being presented at the AAS meeting. We invite all COS users to review these to find out about the latest developments and future plans for COS. Below we include links to the posters and summaries. Additionally, all COS posters are archived on the COS poster page.

350.01 Updated Status and Performance of the Cosmic Origins Spectrograph (T. Fischer and the COS Team)

We present recent calibration work of interest to COS users and proposers. Specifically, COS FUV blue mode observations (i.e. G130M spectra centered at 1055 and 1096 Angstroms) have been recalibrated, with improvements to the flux calibration, time-dependent sensitivity (TDS) calibration, and wavelength calibration. Additionally, we describe the delivery of a new FUV TDS reference file (TDSTAB). Finally, we discuss recent improvements in the CalCOS pipeline that reduce uncertainties in datasets with low count rates.

326.08 Enabling Ultraviolet Science into the 2030's with the Cosmic Origins Spectrograph (M. Rafelski, B. James, and the COS Team)

To mitigate the effect of gain sag and provide the community with access to unsagged regions of the FUV detector, the location of the COS FUV spectrum is periodically moved to new locations on the detector (called lifetime positions or LP). The COS/FUV channel is currently operating at its fourth LP on the detector (LP4), and ongoing work will enable the commissioning of future LPs. We present updates on the current status of COS and exciting new developments that will extend the lifetime of COS into the 2030's. This is enabled by using new regions on the detector and operating the FUV channel in a hybrid LP mode with different settings at different positions on the FUV detector.

For AAS attendees, there will be a poster viewing for Poster 350.01 at 4:10 pm - 5:40 pm on Wednesday, January 13th, and a presentation for Poster 326.08 at 5:30 pm-5:40 pm also on January 13th.


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New Dark Rates Adopted for ETC v29.1

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.

The FUV dark rates adopted by ETC version 29.1 have changed only slightly since the previous version. The new dark rates are 1.99E-6 counts/sec/pixel (down by 1%) and 1.91E-6 counts/sec/pixel (up by 3%) for FUVA and FUVB, respectively. The dark rates for Spectroscopic Target Acquisition are now 3.02E-6 counts/sec/pixel (unchanged) and 3.04E-6 counts/sec/pixel (up by 2%) for FUVA and FUVB, respectively.

The NUV dark rate adopted by ETC version 29.1 has been raised to 1.13E-3 counts/sec/pixel (up by 2%).

PIs are strongly encouraged to use the latest version of the ETC for determining exposure times for use in their Phase II proposals. 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.


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