High-resolution Infrared Spectrograph for Exoplanet Characterization with the Keck and Thirty Meter Telescopes

Abstract

HISPEC (High-resolution Infrared Spectrograph for Exoplanet Characterization) is a proposed diffractionlimited spectrograph for the W.M. Keck Observatory, and a pathfinder for the MODHIS facility project (Multi-Object Diffraction-limited High-resolution Infrared Spectrograph) on the Thirty Meter Telescope. HISPEC/MODHIS builds on diffraction-limited spectrograph designs such as Palomar-PARVI and LBTiLocator, both of which rely on adaptively corrected single-mode fiber feeds. Seeing-limited highresolution spectrographs, by virtue of the conservation of beam etendue, grow in volume following a D 3 power law (D is the telescope diameter), and are subject to daunting challenges associated with their large size (e.g. mechanical and thermal stability). Diffraction-limited spectrographs fed by single mode fibers are decoupled from the telescope input, and are orders of magnitude more compact and have intrinsically more stable line spread functions. On the flip side, their efficiency is directly proportional to the performance of the adaptive optics (AO) system. AO technologies have matured rapidly over the past two decades, becoming mainstream on current large ground-based telescopes and baselined for future extremely large telescopes. HISPEC/MODHIS will take R>100,000 spectra of a few objects in a 10” field-of-view sampled at the diffraction limit (10 mas scale), simultaneously from 0.95 to 2.4 µm (y band to K band). The scientific scope ranges from exoplanet infrared precision radial velocities, transit and close-in exoplanet spectroscopy (atmospheric composition and dynamics, RM effect), spectroscopy of directly imaged planets (atmospheric composition, spin measurements, Doppler imaging), brown dwarf characterization, stellar physics/chemistry, proto-planetary disk kinematics/composition, Solar system (e.g. comets), extragalactic science, and cosmology. HISPEC/MODHIS features a compact and cost-effective design optimized to fully exploit the existing Keck-AO and future TMT-NFIRAOS infrastructures and boost the scientific reach of both Keck Observatory and TMT soon after first light.