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.
The High-Resolution Infrared Spectrograph for Exoplanet Characterization (HISPEC) is a new instrument for the W. M. Keck Observatory that enables R~100,000 spectroscopy simultaneously across the y, J, H, and K astronomical bands (0.98-2.5μm). The Front-End Instrument (FEI) steers the adaptive optics corrected beam delivered by Keck to single-mode fibers used to route the light to the spectrographs. This paper shows the structural (static and dynamic scenarios) and thermal (cryogenic H2RG tracking camera) design of the Front-End Instrument (FEI).
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.
The High-Resolution Infrared Spectrograph for Exoplanet Characterization (HISPEC) is a new instrument for the W. M. Keck Observatory that enables R∼100,000 spectroscopy simultaneously across the y, J, H, and K astronomical bands (0.98-2.5 μm). The front-end instrument steers the adaptive optics corrected beam delivered by Keck to single-mode fibers used to route the light to the spectrographs. The basic architecture of the front-end instrument leverages from the design from the Keck Planet Imager and Characterizer where a tracking camera is used to monitor the location of the target and send commands to a tip/tilt mirror mounted in a pupil plane, which aligns the beam with the fiber in the downstream focal plane. The system will have an atmospheric dispersion corrector to minimize chromatic smearing of the PSF, phase induced amplitude apodization optics to mitigate coupling limitations imposed by the pupil geometry, and vortex masks to enable vortex fiber nulling. The front-end instrument will utilize a Teledyne H2RG for tracking allowing for the ability to guide on targets as faint as 15th magnitude and for tip/tilt control up to 500 Hz on brighter targets. In this paper we provide an overview of the detailed design of the front-end instrument and elucidate the design choices driven by de-risking exercises. We will describe our plan to utilize the J-H gap for tracking which will allow for uninterrupted science for a large population of targets. We present how the front-end instrument will be integrated into the Keck adaptive optics bench to allow for easy removal and cable management. Finally, we provide an update on the project status and the timeline for the sub-system.
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.
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