Cryoscope will be a diffraction limited 1.2m telescope with 50 deg2 field of view contributing less thermal background than the dark K band sky at the Concordia Base in Antarctica. Cryoscope Pathfinder is 26cm version which has been built and is soon to be deployed at Dome C to retire technical risks. This paper reviews key design choices that make the substantial increase in field of view and reduction in thermal background possible. We address the technical challenges associated with the new approach and with operation over the > 100 C temperature difference between laboratory and winter at Dome C. The athermal window support and bonding are described. The baffling and thermal models are presented along with strategies for preventing condensation on the large vacuum window which radiates significant heat into the cryogenically cooled telescope. We conclude with a vision for a modular prefabricated tower to raise the telescope above the 25-30 m inversion layer, and an approach to image stabilization, so that diffraction limited imaging can be achieved over the full field of view.
Since the start of science operations in 1993, the twin 10-meter W. M. Keck Observatory (WMKO) telescopes have continued to maximize their scientific impact to produce transformative discoveries that keep the U.S. observing community on the frontiers of astronomical research. Upgraded capabilities and new instrumentation are provided though collaborative partnerships primarily with the Caltech and University of California instrument development teams and through additional collaborations with the University of Notre Dame, the University of Hawaii, Swinburne University of Technology, industry, and other organizations. This paper summarizes the status and performance of observatory infrastructure projects, technology upgrades, and new additions to the suite of observatory instrumentation. We also provide a status of instrumentation projects in early and advanced stages of development that will achieve the goals and objectives summarized in the 2023 Keck Observatory strategic plan. Developed in collaboration with the WMKO science community, the Keck strategic plan sets our sites on 2035 and meets goals identified in the Astro2020 Decadal Survey.
Cryoscope is a diffraction-limited 26 cm aperture wide-field NIR telescope that uses optics mounted in a cryogenic environment to minimize background radiation from thermal emission. Different mounting strategies were adopted for each of the optical elements: primary mirror, field flatteners, and meniscus corrector lenses. The opto-mechanical design and mounting schemes are to allow stress-free radial expansion of the optics when transitioning to a cryogenic environment from lab ambient temperatures while providing a factor of safety from other sources of stress such as differential pressure and gravity loads. One of the lens elements provides the vacuum seal to the cryostat which along with a stress-free mounting scheme needs to have permeation characteristics no worse than a typical fluorosilicone O-ring to maintain a low pressure (~1 µTorr) vacuum environment that can withstand the harsh -80C environment for deployment at Dome C in the Antarctic. We present the design, analysis, and prototyping results for the lens mounting schemes in Cryoscope that can be scaled by 4x to 1-m class telescopes.
LRIS-2 (Low Resolution Imaging Spectrometer) is a planned Cassegrain mounted spectrometer at WM Keck Observatory with on-axis field of view of 5’x10’ in two simultaneous wavelength channels covering 310-1000nm at R~1500 in a single exposure. This instrument will replace its precursor whose optomechanical design and aging mechanisms preclude further improvements in its stability and reliability. The instrument has two science cameras for Red (~550-1000nm) and blue (~310-550nm) channels, each comprising of six lens elements. This poster details the design scheme and thermo-structural analysis for the lens mounting strategy. The design features 6 passive radial thermal compensators, addressing differential thermal expansion between Aluminum cell and the lens. A comparative assessment among three material candidates for the compensators resulted in an optimized geometry and hertzian contact stress using finite element analysis (FEA). A prototype was developed to validate the design accuracy and repeatability.
HISPEC (High-resolution Infrared Spectrograph for Exoplanet Characterization) is an infrared (0.98 to 2.46 microns) cross-dispersed, R=100,000 single-mode fiber-fed diffraction-limited echellette spectrograph for the Keck II telescope’s adaptive optics (AO) system. MODHIS (Multi-Objective Diffraction-limited High-resolution Infrared Spectrograph) shares similar specifications as HISPEC while being optimized for TMT’s first-light AO system NFIRAOS. Keck-HISPEC, currently in full-scale development and slated for first light in 2026, and TMTMODHIS, currently in conceptual design phase, will provide increasingly compelling science capabilities from exoplanet atmosphere characterization through both transit and direct high-contrast spectroscopy, to detection and mass measurements through infrared precision radial velocity (RV). The science cases include the precise RV measurements of stars orbiting the Galactic Center, Solar System studies, and the chemodynamical history of nearby dwarf galaxies and the galactic halo.
We present a concept design for a next generation low resolution, wide-field, optical imaging spectrometer intended to continue the legacy of LRIS as the premier workhorse optical spectrometer on the Keck I telescope, which we notionally call LRIS-2. The original LRIS continues to be used an average of more than 100 nights per year while maintaining a remarkably high publication rate, neither of which shows any signs of diminishing with time. Nevertheless, LRIS was commissioned ∼30 years ago, and its opto-mechanical design and aging mechanisms preclude further improvements in its stability and reliability. This paper presents the conceptual design of a state-of-the-art instrument combining the core capabilities and scientific versatility of LRIS with substantial improvements in throughput, image quality, stability, and on-sky efficiency. In this paper, we present a concept for a versatile imaging spectrometer with an on-axis field of view of 10′×5′ in two simultaneous wavelength channels that together cover 3100 – 10,300Å at R∼1500 in a single exposure, with a multiplex factor of 70. The optical design delivers total spectroscopic throughput close to 60%, a gain over the current LRIS of 30-100%. The design is able to benefit from significant engineering heritage from LRIS-B, KCWI, KCRM, and TMT-WFOS projects.
For the fifth Sloan Digital Sky Survey, SDSS-V, we moved one of the two SDSS BOSS spectrographs from Apache Point Observatory in New Mexico to Las Campanas Observatory in Chile, giving us dual-hemisphere coverage. Modifications for connecting to a new robotic fiber positioner included replacing the old fiber slit with a monolithic fiber slit made of a precision-machined glass mount presenting 528 fibers. To construct this slit, V-grooves were cut into a borosilicate glass substrate and fibers were glued into them under a cover plate. This glass slit was then attached to an Alloy 39 (steel) flexure, which in turn was affixed to a thin slit plate made of cast aluminum for insertion into the spectrograph. Because our existing spare parts inventory would not support two distant locations, and because many parts were no longer manufactured, some spectrograph subsystems were replaced with new components or designs.
HISPEC is a new, high-resolution near-infrared spectrograph being designed for the W.M. Keck II telescope. By offering single-shot, R 100,000 spectroscopy between 0.98 – 2.5 μm, HISPEC will enable spectroscopy of transiting and non-transiting exoplanets in close orbits, direct high-contrast detection and spectroscopy of spatially separated substellar companions, and exoplanet dynamical mass and orbit measurements using precision radial velocity monitoring calibrated with a suite of state-of-the-art absolute and relative wavelength references. MODHIS is the counterpart to HISPEC for the Thirty Meter Telescope and is being developed in parallel with similar scientific goals. In this proceeding, we provide a brief overview of the current design of both instruments, and the requirements for the two spectrographs as guided by the scientific goals for each. We then outline the current science case for HISPEC and MODHIS, with focuses on the science enabled for exoplanet discovery and characterization. We also provide updated sensitivity curves for both instruments, in terms of both signal-to-noise ratio and predicted radial velocity precision.
KOSMOS is a low-resolution, long-slit, optical spectrograph that has been upgraded at the University of Washington for its move from Kitt Peak National Observatory’s Mayall 4-m telescope to the Apache Point Observatory’s ARC 3.5-m telescope. One of the additions to KOSMOS is a slitviewer, which requires the fabrication of reflective slits, as KOSMOS previously used matte slits machined via wire electrical discharge machining. We explore an innovative method of slit fabrication using nanofabrication methods and compare the slit edge roughness, width uniformity, and the resulting scattering of the new fabricated slits to the original slits. We find the kerf surface of the chemically etched reflective silicon slits are generally smoother than the machined matte slits, with an upper limit average roughness of 0.42 ± 0.03 μm versus 1.06 ± 0.04 μm, respectively. The etched slits have width standard deviations of 6 ± 3 μm versus 10 ± 6 μm, respectively. The scattering for the chemically etched slits is higher than that of the machined slits, showing that the reflectivity is the major contributor to scattering, not the roughness. This scattering, however, can be effectively reduced to zero with proper background subtraction. As slit widths increase, scattering increases for both types of slits, as expected. Future work will consist of testing and comparing the throughput and spectrophotometric data quality of these nanofabricated slits to the machined slits with on-sky data, in addition to making the etched slits more robust against breakage and finalizing the slit manufacturing process.
SIGHT is a new approach to adaptive optics emphasizing panchromatic image sharpening from 360 nm – 2500 nm with specific intent to increase spectrograph observing sensitivity and operational efficiency. Utilizing a single, pilot-safe ultraviolet (invisible) Rayleigh laser guide star (LGS), we prioritize all-sky seeing enhancement and energy concentration, with minimal observing overheads, over absolute spatial resolution. We accomplish this by releasing the system requirement for natural guide star (NGS) tip-tilt wavefront sensing, seeking instead partial tip-tilt information obtainable with LGS telemetry alone. By implementing an ultra-compact (17 cm x 20 cm x 56 cm) parfocal AO relay installed permanently ahead of the Cassegrain focus, we enable high-spatial-frequency AO correction over a field of view of up to 30 arcseconds in diameter. The development of AO differentiated for specific scientific goals represents a further maturation of AO technology beyond the gilded cage of Strehl ratio
HISPEC (High-resolution Infrared Spectrograph for Exoplanet Characterization) is an infrared (0.95 to 2.46 microns) cross-dispersed, R=100,000 single-mode fiber-fed diffraction-limited echellette spectrograph for the Keck II telescope’s adaptive optics (AO) system. MODHIS (Multi-Objective Diffraction-limited High-resolution Infrared Spectrograph) shares similar specifications as HISPEC while being optimized for TMT’s first-light AO system NFIRAOS. Keck-HISPEC (2025) then TMT-MODHIS will provide increasingly compelling science capabilities from exoplanet atmosphere characterization through both transit and direct high-contrast spectroscopy, to detection and mass measurements through infrared precision radial velocity (RV). The science cases include the precise RV measurements of stars orbiting the Galactic Center, Solar System studies, and the chemodynamical history of nearby dwarf galaxies and the galactic halo.
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