The On-Orbit Performance of the Cosmic Origins Spectrograph (original) (raw)
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The Cosmic Origins Spectrograph: on-orbit instrument performance
Astrophysics and Space Science, 2011
The Cosmic Origins Spectrograph (COS) was installed in the Hubble Space Telescope in May, 2009 as part of Servicing Mission 4 to provide high sensitivity, medium and low resolution spectroscopy at farand near-ultraviolet wavelengths (FUV, NUV). COS is the most sensitive FUV/NUV spectrograph flown to date, spanning the wavelength range from 900Å to 3200Å with peak effective area approaching 3000 cm 2 . This paper describes instrument design, the results of the Servicing Mission Orbital Verification (SMOV), and the ongoing performance monitoring program.
The Cosmic Origins Spectrograph: Design, Preflight Performance and Science Goals
2009
The Cosmic Origins Spectrograph (COS) is a new ultraviolet spectrograph which will be installed into the Hubble Space Telescope (HST) as part of the upcoming Servicing Mission 4. COS will be the most sensitive ultraviolet spectrograph ever flown aboard HST, and is optimized for observing faint, point source targets at low and moderate spectral resolutions (R˜ 1500-3500 and 16,000-20,000) at wavelengths ranging from 115 nm to 320 nm. The principal scientific objectives of the mission include the study of the origins of large-scale structures in the universe, the formation and evolution of galaxies, the origin of stellar and planetary systems and the cold interstellar medium. We will present the instrument design, preflight performance, projected on-orbit capabilities, and the key scientific objectives of the mission.
2003
COS has two distinct ultraviolet channels covering the spectral range from 1150Å to 3200Å. The NUV channel covers the range from 1700Å to 3200Å and uses the Hubble Space Telescopes STIS spare MAMA. The FUV channel uses a micro channel plate detector with a cross-delay line readout system to cover the range from 1150Å to 1900Å. Due to the analog nature of the readout electronics of the FUV detector, this system is sensitive to temperature variations and has nonuniform pixel size across its sensitive area. We present a step-by-step description of the calibration process required to transform raw data from the COS into fully corrected and calibrated spectra ready for scientific analysis. Initial simulated raw COS data is used to demonstrate the calibration process.
Wavelength Calibration of the Cosmic Origins Spectrograph
2010
The Cosmic Origins Spectrograph (COS) was installed during the most recent servicing mission of the Hubble Space Telescope. The FUV channel, 10 to 30 times more sensitive than STIS, covers the wavelength range from 1150 to 1800 A with the medium resolution gratings (G130M/G160M) and from 900 to 2400 A with the low resolution grating (G140L). The medium resolution gratings in the NUV channel (G185M/G225M/G285M) cover 1700 to 3200 A, while the low resolution grating (G230L) covers 1700 to 3200 A. We describe the wavelength calibration of the FUV and NUV channels, which uses a combination of ground and on-orbit data obtained during SMOV. We consider the effect of drift of the Optics Select Mechanisms (OSM) on the wavelength scales and describe how the onboard wavecal lamps allow us to correct for the OSM drift. We report the accuracy achieved with the current wavelength calibration strategy and summarize our cycle 17 wavelength calibration plans.
THE COSMIC ORIGINS SPECTROGRAPH
The Astrophysical Journal, 2012
The Cosmic Origins Spectrograph (COS) is a moderate-resolution spectrograph with unprecedented sensitivity that was installed into the Hubble Space Telescope (HST) in May 2009, during HST Servicing Mission 4 (STS-125). We present the design philosophy and summarize the key characteristics of the instrument that will be of interest to potential observers. For faint targets, with flux F λ ≈ 1.0 × 10 −14 erg cm −2 s −1Å−1 , COS can achieve comparable signal to noise (when compared to STIS echelle modes) in 1-2% of the observing time. This has led to a significant increase in the total data volume and data quality available to the community. For example, in the first 20 months of science operation (September 2009 -June 2011) the cumulative redshift pathlength of extragalactic sight lines sampled by COS is 9 times that sampled at moderate resolution in 19 previous years of Hubble observations. COS programs have observed 214 distinct lines of sight suitable for study of the intergalactic medium as of June 2011. COS has measured, for the first time with high reliability, broad Lyα absorbers and Ne VIII in the intergalactic medium, and observed the He II reionization epoch along multiple sightlines. COS has detected the first CO emission and absorption in the UV spectra of low-mass circumstellar disks at the epoch of giant planet formation, and detected multiple ionization states of metals in extra-solar planetary atmospheres. In the coming years, COS will continue its census of intergalactic gas, probe galactic and cosmic structure, and explore physics in our solar system and Galaxy.
Cosmic Origins Spectrograph: On-Orbit Performance of Target Acquisitions
Hubble After Sm4 Preparing Jwst, 2010
COS is a slit-less spectrograph with a very small aperture (R=1.25). To achieve the desired wavelength accuracies, HST+COS must center the target to within 0.1 of the center of the aperture for the FUV channel, and 0.04 for NUV. During SMOV and early Cycle 17 we fine-tuned the COS target acquisition (TA) procedures to exceed this accuracy for all three COS TA modes; NUV imaging, NUV spectroscopic, and FUV spectroscopic. In Cycle 17, we also adjusted the COSto-FGS offsets in the SIAF file. This allows us to recommend skipping the time consuming ACQ/SEARCH in cases where the target coordinates are well known. Here we will compare the on-orbit performance of all COS TA modes in terms of centering accuracy, efficiency, and required signal-to-noise (S/N).
The FUV detector for the cosmic origins spectrograph on the Hubble Space Telescope
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2002
The Cosmic Origins Spectrograph (COS) is a high throughput spectrometer that will be placed on the Hubble Space Telescope (HST) during the last servicing mission in the year 2003. COS will be the most sensitive UV spectrograph ever flown aboard HST and will investigate such fundamental issues as the ionization and baryon content of the intergalactic medium and the origin of large scale structure of the Universe. The driving design goal for COS is to maximize throughput at a moderate spectral resolution of ≥ 20,000 using optics with very few reflections and detectors with high quantum efficiency in two bandpass channels: FUV (1150-1775Å) and NUV (1750-3200Å).
Far-UV sensitivity of the Cosmic Origins Spectrograph
2009
We demonstrate that the G140L segment B channel of the Cosmic Origins Spectrograph (COS) recently installed on the Hubble Space Telescope (HST) has an effective area consistent with ∼ 10 cm 2 in the bandpass between the Lyman edge at 912Å and Lyman β, rising to a peak in excess of 1000 cm 2 longward of 1130Å. This is a new wavelength regime for HST and will allow opportunities for unique science investigations. In particular, investigations seeking to quantify the escape fraction of Lyman continuum photons from galaxies at low redshift, determine the scale-length of the hardness variation in the metagalactic ionizing background over the redshift range 2 < z 2.8, measure the ratio of CO to H 2 in dense interstellar environments with A V > 3, or harness the high temperature diagnostic power of the O VI λλ 1032, 1038 doublet can now be carried out with unprecedented sensitivity.
Science Investigations Enabled by the Far-UV Sensitivity of the Cosmic Origins Spectrograph
2010
We demonstrate that the G140L segment B channel of the Cosmic Origins Spectrograph (COS) recently installed on the Hubble Space Telescope (HST) has an effective area consistent with ∼ 10 cm in the bandpass between the Lyman edge at 912 Å and Lyman β, rising to a peak in excess of 1000 cm longward of 1130 Å. This is a new wavelength regime for HST and will allow opportunities for unique science investigations. In particular, investigations seeking to quantify the escape fraction of Lyman continuum photons from galaxies at low redshift, determine the scale-length of the hardness variation in the metagalactic ionizing background over the redshift range 2 < z . 2.8, measure the ratio of CO to H2 in dense interstellar environments with AV > 3, or harness the high temperature diagnostic power of the O VI λλ 1032, 1038 doublet can now be carried out with unprecedented sensitivity. Subject headings: instrumentation: spectrographs, ultraviolet: general
Far-Ultraviolet Sensitivity of the Cosmic Origins Spectrograph
Astrophysical Journal Letters, 2010
We demonstrate that the G140L Segment B channel of the Cosmic Origins Spectrograph recently installed on the Hubble Space Telescope (HST) has an effective area consistent with ~10 cm2 in the bandpass between the Lyman edge at 912 Å and Lyman beta, rising to a peak in excess of 1000 cm2 longward of 1130 Å. This is a new wavelength