Six-year progress of the InfraRed Doppler (IRD) instrument for the Subaru Telescope

Abstract

The InfraRed Doppler (IRD) instrument is the Subaru telescope's high-resolution (R > 70,000) spectrograph covering wavelengths from 1000 to 1700 nm. A laser frequency comb (LFC) spectrum simultaneously obtained with an object spectrum calibrates wavelength shifts caused by instrumental instability. We originally developed IRD to carry out precision radial velocity (RV) measurements at near-infrared wavelengths. The wide wavelength coverage of IRD, and the large mirror (8.2 m) of the Subaru Telescope enables IRD to provide the best sensitivities to detect a planet orbiting a cool M-type star. The first science operation of IRD was conducted in 2018 and the large strategic blind survey for planets orbiting cool M-type stars started in 2019. Since then, there have been many observations not only for exoplanet category but also for stellar physics, Galaxy, and high-energy astrophysics. IRD spectroscopy allowed for characterizing exoplanet atmospheres by measuring OH emissions, He absorptions, and spin-orbit obliquities. The IRD survey discovered a super-Earth in orbit near a habitable zone of Ross 508. The IRD RV measurements for many systems that host transiting planets, including TOI-2285 b and Gliese 12 b, helped confirm those and determine or constrain their masses. Using REACH, IRD can be combined with the extreme adaptive optics SCExAO, enabling the use of a single-mode fiber and characterizations of faint sub-stellar companions orbiting bright stars. In this proceeding paper, we review and highlight the scientific results achieved by the IRD observations.