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.
Transmission spectroscopy is a powerful observing technique to probe the atmospheric spectrum of an exoplanet that transits its host star. Low resolution transmission spectroscopy can probe both spectral features and the continuum of a planet's atmosphere, but is difficult to do from the ground due to Earth's atmosphere. Here we present HIRAX, a ground-based instrument capable of imaging a system simultaneously in multiple narrowband filters to perform transmission spectroscopy in three 3Å wide bands. HIRAX uses self-referenced bandpasses and a simple imaging design to reduce systematic effects related to Earth's atmosphere and probe an exoplanet transmission spectrum at a few stable wavelengths. HIRAX has been designed for characterizing the sodium doublet (5889.9Å and 5895.9Å) in hot Jupiter atmospheres using the Hale telescope at Palomar Observatory. Here we present the motivation for HIRAX, detail its optical and mechanical design, and present several requirements we imposed on HIRAX in order for it to achieve a photometric precision near the photon limit. We also detail the status of HIRAX and future observing plans.
Cryoscope Pathfinder is a 16 deg2 field-of-view (FoV) infrared telescope, operating in the photometric Kdark bandpass (2.35-2.5 μm). With a plate scale of 7.1′′ per 18 μm pixel on a 2048×2048 Teledyne H2RG detector array, Cryoscope Pathfinder will be the widest and deepest near-infrared imager of its kind in the K-band. A spherical primary mirror is utilized but unlike classical Schmidt designs, Cryoscope employs two fused silica meniscus lenses located on either side of the entrance pupil whereas a Schmidt telescope uses two nearly flat aspheric plates of different glass material located at a distance equal to twice the focal length from the vertex of the primary mirror. An achromatic doublet tuned to the passband delivers a flat focal plane even at large FoV. The convex meniscus element can support atmospheric pressure, allowing the entire optical path to be evacuated and cooled to 80 K to reduce thermal self-emission in a design delivering two orders of magnitude greater FoV than existing ground-based infrared telescopes. We report room temperature performance measurements, which confirm that manufacturing and alignment errors do not significantly compromise the excellent wide-field performance predicted by optical models. Interferometry in a warm bench-test setup has demonstrated on- and off-axis Strehl of 0.95 in the operating bandpass of the telescope, with co-alignment errors within ±0.2 mm. Mechanical assembly of the cryostat is now underway. Cold tests will then assess the performance of the system under vacuum and measure the thermal self-emission by capping the entrance aperture with a narcissus mirror. On-sky tests at Caltech will then be used to demonstrate focus control and PSF image quality using bright star standards over the full FoV. Cryoscope Pathfinder will be deployed to Dome C, Antarctica in December 2024 where it will benefit from infrared sky brightnesses more than 30 times darker than at temperate latitudes.
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.
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