The InfraRed Doppler (IRD) spectrograph can provide high-resolution (R > 70,000) spectra over 1000-1700 nm with stable wavelength calibrations thanks to a dedicated laser frequency comb. Since the first science operation on the Subaru 8.2-m Telescope in 2018, IRD has been extensively used for observations, in which the main field is exoplanet but some studies cover the fields of Galaxy evolution and compact object. One of the main outputs is the discovery of a super-Earth close to the habitable zone of cool M dwarf Ross 508. IRD was also used to constrain the masses of many planets identified with TESS, and to identify the atomic/molecular features of transiting planets. Recently, the extreme adaptive optics system, SCExAO, can be combined with IRD to directly characterize a substellar companion with high-contrast and high-resolution spectroscopy. We here highlight and summarize the outputs obtained via the six-year operation of IRD.
The South Africa Near-infrared Doppler instrument (SAND) is a time-stable high-dispersion spectrograph, covering the z- and Y-bands simultaneously (849 - 1085 nm) with the maximum spectral resolution of ∼60,000. We aim to monitor the radial velocity of M-dwarfs with the precision of a few m/s level, which enables us to search for habitable exoplanets. Our another scientific motivation is the statistical investigation of young planets and stellar atmosphere to comprehensively understand the formation senario of stellar systems. We are planning to install the SAND to telescopes at the South African Astronomical Observatory (SAAO) in Sutherland, since the Southern sky covers plentiful stellar associations with young stars. The SAND is a fiber-fed spectrograph, and we can change telescope used to collect the star light by switching the fiber connection. It will be operated mainly with two telescopes: the Prime-focus Infrared Microlensing Experience telescope (PRIME) and the InfraRed Survey Facility (IRSF), which both are managed by universities in Japan. This strategy of using multiple telescopes gives us opportunities of frequent and long-term observations, which provides well phase coverage in radial velocity monitoring and results in non-bias search for exoplanets. Most of the components used in the spectrograph and the fiber injection module have been fabricated. We will present the detailed status and recent progress: designing the fiber injection module and the thermal control system, examination of fiber characteristics, and estimating our target candidates.
We assessed the impact of Earth’s atmospheric absorption lines, known as telluric contamination, on near-infrared radial velocity (RV) measurements using IRD/Subaru. We focused on the telluric removal process implemented in the RV pipeline for IRD data, which works in two phases: the creation of a stellar template spectrum and the measurement of RVs through a forward modeling approach. Our analysis revealed that discrepancies of approximately 1% exist between the observed telluric standard star’s spectra and theoretical telluric spectra, both used within the RV pipeline. These discrepancies are particularly significant in regions with strong water vapor absorption. Additionally, we investigated the impacts of residual tellurics on RV measurements through mock spectrum analysis. By comparing RV values derived from mock spectra made with either theoretical or observed tellurics, we found that residual tellurics can introduce an additional scatter of at least 1 m/s in RV measurements. Our findings highlight the necessity for improved telluric removal methods in the near-infrared spectrum to achieve precise RV measurements critical for detecting small-mass planets.
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