2 research outputs found
Assessing telluric correction methods for Na detections with high-resolution exoplanet transmission spectroscopy.
Using high-resolution ground-based transmission spectroscopy to probe
exoplanetary atmospheres is difficult due to the inherent telluric
contamination from absorption in Earth's atmosphere. A variety of methods have
previously been used to remove telluric features in the optical regime and
calculate the planetary transmission spectrum. In this paper we present and
compare two such methods, specifically focusing on Na detections using
high-resolution optical transmission spectra: (a) calculating the telluric
absorption empirically based on the airmass, and (b) using a model of the
Earth's transmission spectrum. We test these methods on the transmission
spectrum of the hot Jupiter HD 189733 b using archival data obtained with the
HARPS spectrograph during three transits. Using models for Centre-to-Limb
Variation and the Rossiter-McLaughlin effect, spurious signals which are
imprinted within the transmission spectrum are reduced. We find that correcting
tellurics with an atmospheric model of the Earth is more robust and produces
consistent results when applied to data from different nights with changing
atmospheric conditions. We confirm the detection of sodium in the atmosphere of
HD 189733 b, with doublet line contrasts of -0.64 0.07 % (D2) and -0.53
0.07 % (D1). The average line contrast corresponds to an effective
photosphere in the Na line located around 1.13 . We also confirm an
overall blueshift of the line centroids corresponding to net atmospheric
eastward winds with a speed of 1.8 1.2 km/s. Our study highlights the
importance of accurate telluric removal for consistent and reliable
characterisation of exoplanetary atmospheres using high-resolution transmission
spectroscopy
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High-resolution Spectroscopic Reconnaissance of a Temperate Sub-Neptune
Abstract
The study of temperate sub-Neptunes is the new frontier in exoplanetary science. A major development in the past year has been the first detection of carbon-bearing molecules in the atmosphere of a temperate sub-Neptune, K2-18 b, a possible Hycean world, with the James Webb Space Telescope (JWST). The JWST is poised to characterize the atmospheres of several other such planets, with important implications for planetary processes in the temperate regime. Meanwhile, ground-based high-resolution spectroscopy has been highly successful in detecting chemical signatures of giant exoplanets, though low-mass planets have remained elusive. In the present work, we report the atmospheric reconnaissance of a temperate sub-Neptune, TOI-732 c, using ground-based high-resolution transmission spectroscopy. The long orbital period and the low systemic velocity result in a low planetary radial velocity during transit, making this system a valuable test bed for high-resolution spectroscopy of temperate sub-Neptunes. We observe high-resolution time-series spectroscopy in the H and K bands during the planetary transit with the IGRINS instrument (R ∼ 45,000) on Gemini-South. Using observations from a single transit, we find marginal evidence (2.2σ) for the presence of methane (CH4) in the atmosphere and no evidence for ammonia (NH3) despite its strong detectability for a cloud-free H2-rich atmosphere. We assess our findings using injection tests with different atmospheric scenarios and find them to be consistent with a high CH4/NH3 ratio and/or the presence of high-altitude clouds. Our results demonstrate the capability of Gemini-S/IGRINS for atmospheric characterization of temperate sub-Neptunes and the complementarity between space- and ground-based facilities in this planetary regime.</jats:p