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| LRIS (instrument) | |
|---|---|
| Name | LRIS |
| Caption | LRIS on the Keck I telescope |
| Location | Mauna Kea, Hawaii |
| Altitude | 4205 m |
| Operator | W. M. Keck Observatory |
| Telescope | Keck I |
| Wavelength | Optical, Near-UV, Near-IR (red side) |
| First light | 1993 |
LRIS (instrument) The Low Resolution Imaging Spectrometer (LRIS) is a dual-arm optical spectrograph and imager mounted on the Keck I telescope at W. M. Keck Observatory on Mauna Kea. LRIS provides low- and medium-dispersion spectroscopy and direct imaging for investigations spanning exoplanet atmospheres, galaxy formation, quasar absorption lines, and supernova spectroscopy. The instrument has been central to programs led by teams from institutions such as Caltech, University of California, Berkeley, University of Hawaii, Harvard University, and Institute for Astronomy, University of Hawaii.
LRIS was commissioned in the early 1990s to equip Keck I with simultaneous blue and red spectral coverage for faint-object spectroscopy and deep imaging. Designed to serve surveys pioneered by groups at Caltech and UC Berkeley, LRIS supported large programs including studies by the Sloan Digital Sky Survey community, follow-up of targets from the Hubble Space Telescope deep fields, and spectroscopic confirmation of candidates from the Subaru Deep Field. The instrument's dual-beam architecture and flexible slitmask options made it a workhorse for observers from institutions such as Princeton University, University of California, Santa Cruz, University of Arizona, and University of Chicago.
LRIS comprises a blue arm and a red arm separated by a dichroic beam splitter, enabling simultaneous observations across wavelength bands defined by choices such as the LRIS-B dichroics and red gratings. The optical train includes a Cassegrain-mounted slitmask mechanism, a guider system linked to the Keck Active Optics system, and a set of grisms and gratings sourced from suppliers used by teams at Ball Aerospace and AlliedSignal. Detector systems have included charge-coupled devices provided by manufacturers used by groups at Lawrence Berkeley National Laboratory and Teledyne Imaging Sensors. Mechanical subsystems were designed with contributions from engineers at Jet Propulsion Laboratory and NOAO-affiliated facilities. The instrument supports slit widths down to sub-arcsecond scales for high-resolution work and wide-field imaging with pixel scales useful to teams from Carnegie Observatories and Space Telescope Science Institute.
LRIS offers long-slit spectroscopy, multi-object spectroscopy using custom slitmasks, and direct imaging in multiple bands used by observers from Subaru Telescope collaborations and Gemini Observatory partnerships. Spectral setups enable resolutions appropriate for kinematic studies of galaxy disks, chemical-abundance analyses of globular cluster systems, and redshift determinations for gamma-ray burst afterglows identified by teams at NASA centers. The instrument's sensitivity in the blue is leveraged by investigators from University of California, Santa Barbara and Max Planck Institute for Astronomy for stellar population studies, while the red arm is used by researchers at Imperial College London and University of Cambridge for rest-frame optical emission-line diagnostics of high-redshift sources.
Calibration procedures for LRIS follow practices employed at observatories such as European Southern Observatory and National Optical-Infrared Astronomy Research Laboratory, including bias subtraction, flat-fielding using dome and twilight flats, wavelength calibration with arc lamps common to protocols at NOAO, and flux calibration using spectrophotometric standards maintained by teams at STScI and ESO archives. Data reduction pipelines have been developed by groups at UCO/Lick Observatory, University of California Observatories, and community contributors associated with Astropy and IRAF-based workflows. Advanced reductions incorporate sky-subtraction techniques used by DEEP2 and VVDS survey teams, cosmic-ray rejection routines from Cosmic Ray Removal toolsets, and extraction algorithms similar to those used in SDSS spectroscopic pipelines.
LRIS performance has been enhanced through detector upgrades, new gratings, and improved coating technologies influenced by work at Lawrence Livermore National Laboratory and MIT. Notable upgrades included replacement CCDs to improve quantum efficiency, introduced by collaborations with University of Hawaii instrumentation groups, and an atmospheric dispersion corrector inspired by systems at Gemini Observatory. These improvements increased throughput for faint-object spectroscopy used in programs by Caltech and UC Santa Cruz. Ongoing maintenance is coordinated with technical staff from W. M. Keck Observatory and partner institutions such as NOIRLab and MPIA.
LRIS enabled redshift surveys that mapped large-scale structure in concert with efforts by 2dF Galaxy Redshift Survey and SDSS, confirmed high-redshift quasar candidates discovered by teams at Pan-STARRS and CFHT Legacy Survey, and provided early spectra of Type Ia supernovae used in cosmological distance studies alongside work from Supernova Cosmology Project. LRIS observations contributed to characterizing Lyman-alpha emitters studied by Keck Deep Fields teams, spectroscopic follow-up of Gamma-ray Burst afterglows discovered by Swift Observatory teams, and chemical-abundance measurements in dwarf galaxy satellites linked to investigations by Carnegie Institution scientists. Instrument data underpinned breakthroughs cited by researchers at Harvard–Smithsonian Center for Astrophysics and Yale University.
Operations of LRIS are integrated within the nightly scheduling and technical support framework of W. M. Keck Observatory, with observing time allocated via partner institutions including Caltech, University of California, NASA, and national time allocation committees analogous to those at NOIRLab. Support includes mask design assistance from engineering teams at Keck Observatory Shared Risk Observing, data archival through portals similar to Keck Observatory Archive, and user documentation maintained by instrument scientists affiliated with Caltech and University of California Observatories. Training for observers is provided through workshops run in collaboration with groups at STScI and NOAO.
Category:Spectrographs