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| Keck/OSIRIS | |
|---|---|
| Name | OSIRIS (OH-Suppressing InfraRed Imaging Spectrograph) |
| Facility | W. M. Keck Observatory |
| Location | Mauna Kea, Hawaii |
| Telescope | Keck I |
| Type | Near-infrared integral field spectrograph |
| Wavelength | 1.0–2.4 μm |
| Resolving power | R ≈ 3800–3800 (depending on scale) |
| Spatial scale | 20–100 mas lenslet scales |
| Detectors | HgCdTe array |
| Commissioning | 2005 |
| Status | Operational (upgrades ongoing) |
Keck/OSIRIS
Keck/OSIRIS is a near-infrared integral field spectrograph commissioned at the W. M. Keck Observatory on Mauna Kea, designed for diffraction-limited spectroscopy behind the Keck II adaptive optics system and later used with Keck I and other facilities. It enables simultaneous spatial and spectral sampling for studies of galaxies, stars, planetary systems, active galactic nuclei, and solar system targets, combining technologies from instrument teams including the California Institute of Technology, the University of California, and the W. M. Keck Observatory. The instrument has been central to high-angular-resolution investigations that leverage synergies with facilities such as the Hubble Space Telescope, Atacama Large Millimeter/submillimeter Array, and the Very Large Telescope.
OSIRIS, an acronym for OH-Suppressing InfraRed Imaging Spectrograph, was developed to exploit the diffraction-limited performance of the Keck adaptive optics systems provided by teams at W. M. Keck Observatory, Caltech, and the University of California. The instrument's integral field unit (IFU) uses a lenslet array to sample the focal plane and feed spectra into a cryogenic spectrograph, enabling science programs from resolved stellar populations in the Galactic Center to spatially-resolved kinematics of high-redshift galaxies. It addressed the need for three-dimensional spectroscopy at near-infrared wavelengths during the era of adaptive optics and has been integrated into multi-observatory campaigns with facilities such as Subaru Telescope, Gemini Observatory, and space missions like Spitzer Space Telescope.
OSIRIS employs a cryogenic optical bench housing a lenslet-based IFU, a selectable pupil mask, grating mechanisms, and a HgCdTe detector similar to arrays used on NIRC2 and instruments at Gemini Observatory. Key specifications include coverage across standard near-infrared bands (Y, J, H, K), selectable spectral resolving powers tuned by grating choices, and multiple plate scales (e.g., 20, 35, 50, 100 milliarcseconds) optimized for diffraction-limited and seeing-limited work. The optical design draws on lessons from instruments at European Southern Observatory facilities and includes OH suppression strategies to mitigate sky emission lines characterized in studies with Mauna Kea Observatories. Cryogenic mechanisms and vibration isolation were engineered with input from teams experienced with the Keck Adaptive Optics programs and detector specialists from institutions like University of Hawaii.
OSIRIS supports integral field spectroscopy with selectable spatial sampling, filters for standard photometric bands, and grating configurations for moderate to high resolving power enabling studies of emission-line kinematics and stellar absorption features. Observing modes include on-source IFU mapping, offset sky nodding coordinated with operations staff at W. M. Keck Observatory, and coronagraphic/high-contrast sequences when paired with adaptive optics modules designed by teams at Lawrence Livermore National Laboratory and Jet Propulsion Laboratory. Time-resolved spectroscopy and queue-scheduled programs from consortia including University of California Observatories have exploited OSIRIS for variability studies of brown dwarfs, transiting exoplanets, and reverberation mapping of quasars.
The OSIRIS data reduction pipeline, developed collaboratively by instrument teams and observatory software groups, converts detector readouts into wavelength-calibrated data cubes using routines for dark subtraction, flat-fielding, spectral extraction from lenslet spectra, wavelength solution application referenced to arc lamp exposures, and telluric correction informed by standard star observations. Pipeline evolution incorporated algorithms from the IDL and Python-based communities and adopted best practices demonstrated by teams at Space Telescope Science Institute and European Southern Observatory. Advanced processing steps for sky subtraction, PSF fitting, and mosaic combination have enabled comparison with modeled outputs from radiative transfer codes used by groups at University of Cambridge and Max Planck Institute for Astronomy.
OSIRIS has enabled measurements of stellar orbits in the Galactic Center which constrained parameters related to the supermassive black hole studied by teams associated with UCLA and Max Planck Institute for Extraterrestrial Physics, resolved ionized gas kinematics in active galactic nuclei and starburst galaxies informing feedback models developed at Harvard-Smithsonian Center for Astrophysics, and mapped star-forming clumps in high-redshift galaxies in surveys coordinated with Hubble Space Telescope and ALMA. The instrument contributed to direct spectroscopy of candidate exoplanet companions identified via adaptive optics imaging campaigns led by groups at Carnegie Institution for Science and Institute for Astronomy, University of Hawaii. OSIRIS results have been published alongside complementary spectroscopic datasets from Keck's DEIMOS, NIRSPEC, and comparative analyses with VLT/SINFONI.
Since commissioning, OSIRIS underwent detector replacements, grating and filter refinements, and software upgrades driven by feedback from instrument teams at Caltech, University of California, and observatory engineering groups. Performance improvements targeted readout noise reduction, improved spectral line spread functions, and enhanced throughput informed by laboratory testing at institutions such as Jet Propulsion Laboratory and Lawrence Berkeley National Laboratory. Maintenance periods coordinated with W. M. Keck Observatory operations introduced optimized calibration sequences and integration with evolving adaptive optics modules developed in collaboration with Technische Universität München and other international partners.
OSIRIS is scheduled for shared use through the W. M. Keck Observatory time allocation processes involving partners like Caltech, University of California, and guest observer proposals adjudicated by committees including representatives from NOIRLab-linked institutions. Observing proposals compete in time allocation calls similar to those used by National Science Foundation-funded consortia and international partners. Data access follows observatory policies for proprietary periods, and reduced data products are often deposited in archives managed alongside datasets from instruments like Keck/LRIS and Keck/NIRSPEC for community use.
Category:Near-infrared spectrographs Category:W. M. Keck Observatory instruments