COS (HST)

COS (HST)
Name	COS (HST)
Mission	Hubble Space Telescope
Operator	NASA, European Space Agency
Launch	1990
Instrument type	Ultraviolet spectrograph
Wavelength	Far-ultraviolet, Near-ultraviolet
Resolution	Medium, Medium-High

COS (HST) The Cosmic Origins Spectrograph is an ultraviolet spectrograph installed on the Hubble Space Telescope during STS-125. Designed for high-sensitivity spectroscopy, it extended the ultraviolet capabilities of Hubble Space Telescope and complemented instruments such as the Space Telescope Imaging Spectrograph and the Advanced Camera for Surveys. COS enabled targeted studies of interstellar and intergalactic media, stellar atmospheres, and extragalactic sources, serving investigators affiliated with institutions like Space Telescope Science Institute, NASA Goddard Space Flight Center, and numerous universities.

Overview

COS was developed through partnerships among NASA, the Ball Aerospace, and academic teams led by investigators from Johns Hopkins University, University of Colorado Boulder, and University of California, Berkeley. Installed during the STS-125 servicing mission alongside upgrades that involved crews from the United States Navy-related training programs and mission planners at Johnson Space Center, COS replaced older ultraviolet capabilities and emphasized throughput for faint-source spectroscopy. Its deployment leveraged engineering heritage from programs at Goddard Space Flight Center, optical design advances associated with Lawrence Livermore National Laboratory, and detector innovations linked to University of California, Berkeley teams.

Instrument Design and Components

The COS optical path uses a segmented grating design derived from collaborations between Ball Aerospace and teams at University of Colorado Boulder, employing diffraction gratings similar in heritage to those used on instruments developed at Jet Propulsion Laboratory. The far-ultraviolet (FUV) channel features a two-segment, holographically ruled grating paired with a microchannel plate detector produced with technology from Northrop Grumman subcontractors and laboratory expertise at Southwest Research Institute. The near-ultraviolet (NUV) channel uses a cross-delay line detector and optics built to tolerances influenced by standards from NASA Goddard Space Flight Center optical labs. Mechanical structures incorporate materials and testing protocols from Massachusetts Institute of Technology and Caltech facilities, while thermal control and electronic interfaces follow designs vetted by European Space Agency collaborators. COS includes mechanisms for grating selection and aperture masks, integrating interfaces with Hubble Space Telescope guidance from Space Telescope Science Institute operations teams.

Science Objectives and Capabilities

COS was optimized for high-throughput observations of faint ultraviolet targets to pursue objectives aligned with proposals from researchers at Princeton University, Harvard University, Yale University, University of Chicago, and international partners at University of Cambridge and Max Planck Society. Key goals included characterization of the low-redshift intergalactic medium through absorption-line studies toward quasars discovered in surveys by Sloan Digital Sky Survey, probing circumgalactic media of galaxies cataloged by Two Micron All Sky Survey and Galaxy Evolution Explorer teams, and measuring stellar winds and atmospheres of targets observed by Kepler and GALEX. COS enabled precision measurements of ionic species such as Lyman-alpha absorbers, metal lines associated with O VI and C IV, and molecular transitions relevant to studies connected to Herschel Space Observatory and Spitzer Space Telescope results.

Observing Modes and Performance

COS offers spectroscopic modes including medium-resolution FUV modes and NUV modes with distinct gratings and central wavelength settings used by investigators from Space Telescope Science Institute for programs such as Treasury and Snapshot surveys. The instrument provides high sensitivity with low background, achieving signal-to-noise ratios exploited by teams analyzing data alongside observations from Chandra X-ray Observatory and XMM-Newton. Performance assessments were undertaken with verification programs coordinated by NASA Goddard Space Flight Center and data validation by Space Telescope Science Institute, demonstrating resolving powers suited to absorption-line studies and enabling time-domain spectroscopy used in campaigns coordinated with facilities like Very Large Telescope and Keck Observatory.

Calibration and Data Reduction

Calibration of COS relies on wavelength and flux standards maintained by groups at Space Telescope Science Institute and calibration proposals developed with contributions from National Optical Astronomy Observatory scientists and instrument teams at Ball Aerospace. Pipeline processing is performed by the CALCOS software, maintained by teams associated with Space Telescope Science Institute and NASA Goddard Space Flight Center, and produces calibrated spectra for archival access via the Mikulski Archive for Space Telescopes. Data reduction strategies incorporate tools and techniques refined in concert with researchers from University of California, Santa Cruz, Carnegie Institution for Science, and European Southern Observatory collaborators, addressing fixed-pattern noise, detector backgrounds, and wavelength solution refinements using contemporaneous observations of standards from catalogs maintained by Simbad and survey datasets from Sloan Digital Sky Survey.

Key Discoveries and Scientific Impact

COS enabled breakthroughs in mapping the baryon content of the low-redshift universe through surveys of absorption-line systems toward quasars identified by Sloan Digital Sky Survey and explored the role of galactic outflows and inflows in shaping the circumgalactic medium observed in programs led by teams at Harvard-Smithsonian Center for Astrophysics and University of California, Santa Cruz. Results from COS observations informed models developed at Los Alamos National Laboratory and Max Planck Institute for Astronomy regarding feedback from star formation in galaxies studied by Hubble Deep Field follow-ups and surveys coordinated with ALMA and JWST early science teams. COS data contributed to high-impact publications that influenced theoretical work at Institute for Advanced Study and observational strategies at major observatories including Keck Observatory and Very Large Telescope, establishing COS as a keystone instrument for ultraviolet spectroscopy in the era of multiwavelength astronomy.

Category:Instruments on the Hubble Space Telescope