On-sky Doppler performance of TOU optical very high-resolution spectrograph for detecting low-mass planets

摘要

The TOU robotic, compact very high resolution optical spectrograph (R=100,000, 0.38-0.9 microns) has been fully characterized at the 2 meter Automatic Spectroscopy Telescope (AST) at Fairborn Observatory in Arizona during its pilot survey of 12 bright FGK dwarfs in 2015. This instrument has delivered sub m/s Doppler precision for bright reference stars (e.g., 0.7 m/s for Tau Ceti over 60 days) with 5-30 min exposures and 0.7 m/s long-term instrument stability, which is the best performance among all of the known Doppler spectrographs to our knowledge. This performance was achieved by maintaining the instrument in a very high vacuum of 1 micron torr and about 0.5 mK (RMS) long-term temperature stability through an innovative close-loop instrument bench temperature control. It has discovered a 21 Earth-mass planet (P=43days) around a bright K dwarf and confirmed three super-Earth planetary systems, HD 1461, 190360 and HD 219314. This instrument will be used to conduct the Dharma Planet Survey (DPS) in 2016-2019 to monitor ~100 nearby very bright FGK dwarfs (most of them brighter than V=8) at the dedicated 50-inch Robotic Telescope on Mt. Lemmon. With very high RV precision and high cadence (~100 observations per target randomly spread over 450 days), a large number of rocky planets, including possible habitable ones, are expected to be detected. The survey also provides the largest single homogenous high precision RV sample of nearby stars for studying low mass planet populations and constraining various planet formation models. Instrument on-sky performance is summarized.