Content

Filter

Filter COS ISRs

Listing Results

Results: 113

ISR 2019-14: Cycle 26 COS NUV MAMA Fold Distribution

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.

ISR 2019-13: Cycle 25 COS NUV MAMA Fold Distribution

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.

ISR 2019-12: Cycle 25 COS NUV Spectroscopic Sensitivity Monitor

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.

ISR 2019-10: The Dispersion Solution for the New COS/FUV Cenwave G160M/1533

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.

ISR 2019-09: The Flux Calibration of the New COS/FUV Cenwave G160M/1533

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.

ISR 2019-08: Spectral Extraction of the New COS/FUV G160M/1533 Mode: Extraction, Trace, and Profile Reference Files

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.

ISR 2019-06: Focusing the New COS/FUV Cenwave G160M/1533

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.

ISR 2019-04: The Flux Calibration of the New COS/FUV Cenwave G140L/800

May 13, 2019W. Fischer
We describe the flux calibration of 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. Since relatively few cenwave 800 spectra are yet available, limited testing of the flux calibration accuracy has been possible. With the target used to derive the calibration, we find that it is accurate to 2.32%, within the 5% absolute flux accuracy goal of COS.

ISR 2018-25: Improvements to the COS FUV G130M and G160M Wavelength Solutions at Lifetime Position 4

February 18, 2019R. Plesha
The wavelength dispersion coefficients and zero points of the COS FUV G130M and G160M gratings at each lifetime position (LP1, LP2, LP3, LP4) have been re-derived. In this document we present the analysis behind the improvements of the wavelength solutions for data obtained at LP4 (i.e., beginning on October 2, 2017). With the new dispersion coefficients and zero points, the wavelength solution accuracy has been improved from ∼15 km/s (1 resolution element) to ∼7.5 km/s (0.5 resolution element).

ISR 2018-24: Improvements to the COS FUV G130M and G160M Wavelength Solutions at Lifetime Position 3

March 18, 2019R. Plesha
The wavelength dispersion coefficients and zero points of the COS FUV G130M and G160M gratings at each lifetime position (LP1, LP2, LP3, LP4) have been re-derived. In this document we present the analysis behind the improvements of the wavelength solutions for data obtained at LP3 (i.e., between February 9, 2015 and October 2, 2017). With the new dispersion coefficients and zero points, the wavelength solution accuracy has been improved from ∼15 km/s (1 resolution element) to ∼7.5 km/s (0.5 resolution element).

ISR 2018-23: Improvements to the COS FUV G130M and G160M Wavelength Solutions at Lifetime Position 2

February 18, 2019T. Ake
The wavelength dispersion coefficients and zero points of the COS FUV G130M and G160M gratings at each lifetime position (LP1, LP2, LP3, LP4) have been re-derived. In this document we present the analysis behind the improvements of the wavelength solutions for data obtained at LP2 (i.e., between July 23, 2012 and February 9, 2015) for all central wavelengths except G130M 1055, 1096, and 1222.

ISR 2018-22: Improvements to the COS FUV G130M and G160M Wavelength Solutions at Lifetime Position 1

November 20, 2018R. Plesha
The wavelength dispersion coefficients and zero points of the COS FUV G130M and G160M gratings at each lifetime position (LP1, LP2, LP3, LP4) have been re-derived. In this document we present the analysis behind the improvements of the wavelength solutions for data obtained at LP1 (i.e., before July 2012). Discussions of the methodology used to derive updated wavelength solutions at lifetime positions 2, 3, and 4 are presented in separate documents. In this analysis, we have used archival data of objects that were observed with both COS and an overlapping STIS echelle mode to determine the dispersion coefficient and an initial measurement of the zero point for each standard cenwave setting. The zero points were then refined using archival COS programs where multiple cenwaves were used within a single visit, which provided a better relative alignment between COS modes. The wavelength solution accuracy has been improved from ~15 km/s (1 resolution element) to ~7.5 km/s (0.5 resolution element), with the greatest correction occurring for each grating at the longest cenwaves (i.e., 1327 and 1623).

ISR 2018-21: Traces, Profiles, and Extraction Tables for the COS FUV Channel at Lifetime Position 4

February 14, 2019M. Rafelski
We report on the creation of the COS FUV trace and profile reference files at the fourth lifetime position (LP4). We also describe the creation of spectral extraction tables for the TWOZONE and BOXCAR algorithms. The following is a standalone appendix for 2018-21: Appendix B

ISR 2018-20: Flat Fields and Flux Calibrations for the COS FUV Channel at Lifetime Position 4

September 25, 2018W. Fischer
As part of the calibration of the fourth lifetime position (LP4) of the Cosmic Origins Spectrograph (COS) Far-Ultraviolet (FUV) detector, we derived low-order flat fields (L flats) and sensitivities. To do this, spectra of the star WD 0308-565 were obtained with the G130M, G160M, and G140L gratings, and spectra of the star GD 71 were obtained with the G160M grating, all through the Primary Science Aperture (PSA). Observations were executed with all cenwaves and all FP-POS with the exception of G130M/1055 and G130M/1096, which remained at LP2. The L flats and sensitivities at LP4 were derived with the same method as at LP3. The L flats at LP4 agree with those at LP3 to within ~2%, depending on grating and detector position. The sensitivities at LP4 are as expected after accounting for the previously characterized time-dependent sensitivity of the FUV detector. The relative and absolute flux calibration accuracies at LP4 are within the specifications of 2% and 5%.

ISR 2018-19: On-orbit comparison of the emission line intensities of the COS Pt-Ne Calibration Lamps

August 31, 2018N. Indriolo
There are two platinum-neon (Pt-Ne) hollow cathode lamps on the COS calibration platform that are used for wavelength calibration and target acquisition purposes. Due to differences in optical paths and operating currents the fluxes provided by these lamps (P1 and P2) are not the same. We analyze images and spectra taken with both Pt-Ne lamps to determine the ratio of the lamp fluxes as a function of wavelength. The results are used to compute recommended lamp flash durations should P1 be used for a task normally done with P2, and vice versa. In the event that either Pt-Ne lamp should fail, this analysis provides the starting point for continuing operations with a single working lamp.
LAST UPDATED: 06/10/2019

Please Contact the HST Help Desk with any Questions

https://hsthelp.stsci.edu.