August 21, 2019B. James
We summarize the calibration activities for COS during Cycle 25, which ran from 2017 October through 2018 September. We give an overview of the COS calibration plan and COS usage statistics, and we briefly describe major changes with respect to the previous cycle. High-level executive summaries for each calibration program comprising Cycle 25 are also given. Results of the analysis attached to each program are published in separate ISRs.
August 19, 2019C. Magness
This report summarizes the calibration plan, analysis, and results for the Cycle 25 NUV Dark Monitoring Program (14942) for the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST). Observations for this program were taken for the entirety of Cycle 25, spanning from the end of 2017 October to the end of 2018 October.
August 16, 2019R. Sankrit
The Cycle 25 COS/FUV spectroscopic sensitivity monitor ran from 2017 December to 2019 April. The time-dependent sensitivity (TDS) slopes were found to remain steady and range from 0% to −3%/yr. The program included two additional visits, during which the standard modes were observed at Lifetime Position 3 (LP3) to provide a check on the TDS at the previous lifetime position. It was found that the TDS is largely independent of lifetime position.
August 13, 2019D. Dashtamirova
We summarize the Cycle 25 FUV Dark Monitoring Program for the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST), covering dates 2017 November to 2018 October. We give an overview of the calibration plan and a summary for this calibration program.
August 07, 2019W. Fischer
We report on the monitoring of the zero points of the COS FUV dispersion solutions during Cycle 25 in program 15385. Select cenwaves were monitored for all FUV gratings at Lifetime Position 4. All measured offsets are within the uncertainty thresholds of 6 pixels for G130M/1096, 3 pixels for the other G130M cenwaves, and 9 pixels for the G140L cenwaves.
July 22, 2019W. Fischer
We report on the monitoring of the zero points of the COS NUV dispersion solutions during Cycle 25 in program 15388. Select cenwaves were monitored for all NUV gratings except for G285M, which was removed from the program due to its rapidly declining sensitivity and lack of general observer use since Cycle 21. Comparisons to COS monitoring data obtained in previous cycles indicate internal stability within the allowed ranges. Comparisons to STIS data indicate small but persistent COS offsets of 1–3 pixels toward shorter wavelengths; investigation into this is forthcoming.
June 05, 2019T. Wheeler
We summarize the Cycle 26 COS/NUV fold distribution for the Cosmic Origins Spectrograph's (COS) MAMA detector on the Hubble Space Telescope. The detector micro-channel plate's health state is determined and the results presented.
June 05, 2019T. Wheeler
We summarize the Cycle 25 COS/NUV fold distribution for the Cosmic Origins Spectrograph's (COS) MAMA detector on the Hubble Space Telescope. The detector micro-channel plate's health state is determined and the results presented.
May 30, 2019W. Fischer
The COS NUV detector has a time-dependent sensitivity (TDS) that must be monitored and accounted for in flux calibration. The Cycle 25 NUV TDS monitor shows that the G230L and G185M gratings, which are coated in MgF2, exhibit trends that are consistent with no change in sensitivity. The G225M and G285M gratings, which are bare aluminum, show significant sensitivity declines of −2.84% ± 0.17% per year and −10.43% ± 0.37% per year, respectively. Because the sensitivity of the G285M grating is now very low, we have removed it from subsequent monitoring, and the COS team discourages its use for General Observer (GO) programs.
August 09, 2019D. Dashtamirova
The dark rate of the COS/FUV detector varies across the detector and over time. Detector segment FUVA experiences sporadically increased dark counts along the edges of the detector. This leads to an increased overall dark rate and an artificially inflated background. Here we describe the updates made to the COS Dark Rate Monitor script to better track and account for this effect. We also present changes made to the Lifetime Position 4 (LP4) FUVA background extraction regions to provide a more accurate background subtraction.
April 09, 2019A. Fox
We describe the derivation of the dispersion solution for the new COS/FUV central wavelength (cenwave) setting G160M/1533. The r.m.s. accuracy of the wavelength scale is 1.2 pixels (2.4 km/s) on FUVB and 2.1 pixels (4.2 km/s) on FUVA, similar to the values derived for other G160M cenwaves, and well within the target accuracy of three pixels.
April 08, 2019A. Fox
We describe the derivation of the flux calibration for the new COS/FUV central wavelength (cenwave) setting G160M/1533. We found the flux calibration to be accurate to within 0.6% on FUVB and 0.7% on FUVA, well within the nominal 5% absolute flux accuracy advertised for the G160M modes.
May 14, 2019E. Frazer
We describe the creation of the reference files used in the BOXCAR and TWOZONE extraction algorithms for the new COS/FUV central wavelength setting G160M/1533. We analyze the 2-D profile and spectral trace on each segment of the detector in order to derive the entries for the 1-D spectral extraction, trace correction, profile, and TWOZONE spectral extraction reference files.
June 24, 2019B. James
In Cycle 26 two new central wavelengths (cenwaves) were commissioned for Lifetime Position 4 (LP4) of the COS FUV detector: G160M/1533 and G140L/800. This ISR describes the first stage of this commissioning program for G160M/1533, providing an optimized focus value for the cenwave.
July 10, 2019W. Fischer
We describe the derivation of the dispersion solution for the new COS/FUV central wavelength (cenwave) setting G140L/800, which uses only segment A of the detector to record wavelengths from 800 to 1950 Å at low resolution. We tested the accuracy of the solution by cross-correlating a cenwave 800 spectrum of AV 75 with spectra of the same star obtained 11 days earlier at other cenwaves; nearly all offsets are less than one pixel, small compared to the internal error goal for G140L modes of 4.0 – 6.6 pixels.