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Results: 116

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 2019-05: The Dispersion Solution for the New COS/FUV Cenwave G140L/800

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.

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 2019-03: Spectral Extraction for the New COS/FUV Cenwave G140L/800

July 09, 2019R. Sankrit
The parameters required for the extraction of one-dimensional spectra from two-dimensional spectral images for the new central wavelength mode G140L/800/FUVA were derived from calibration programs executed in 2018 June. In this ISR we describe the the data analysis, present the resulting extraction parameters, and discuss their validation and incorporation into the new reference files.

ISR 2019-01: Focus Sweep for the New COS/FUV Cenwave G140L/800

July 08, 2019R. Sankrit
The focus setting for the new central wavelength mode G140L/800/FUVA was determined based on a focus sweep program executed in 2018 March. In this ISR we describe the focus sweep program and the data analysis, and we present the results.

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).
LAST UPDATED: 06/10/2019

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