[P-EM11] 系外惑星

[PEM11-P18] Subaru/IRD high-resolution spectroscopy of a T-type brown dwarf and investigation of its atmospheric properties with high-resolution spectrum model ExoJAX

*川島 由依¹、河原 創²、笠木 結³、石川 裕之^4,5、増田 賢人⁶、小谷 隆行^4,5、工藤 智幸⁵、平野 照幸^4,5、葛原 昌幸^4,5、Stevanus Nugroho^4,5、John Livingston^4,5、田村 元秀^4,5,7、IRD チーム (1.理化学研究所、2.宇宙科学研究所、3.総合研究大学院大学、4.アストロバイオロジーセンター、5.国立天文台、6.大阪大学、7.東京大学)

キーワード：大気、褐色矮星、系外惑星、高分散分光、スペクトル、組成

Understanding the atmospheres of exoplanets and brown dwarfs holds the key to revealing their formation and evolutionary processes. Brown dwarf atmospheres share composition and temperature with those of extrasolar gas giant planets. In general, brown dwarfs are observable with a higher signal-to-noise ratio when compared to exoplanets. Thus, the observation of brown dwarf atmospheres helps us establish our understanding of various processes in the atmospheres of such temperature and composition, including chemistry, thermal structure, dynamics, and cloud formation. Also, their high-resolution spectra serve as excellent templates for the observational validation of the molecular line lists at such high temperatures. Molecular line lists play a critical role in the detection of chemical species in exoplanet atmospheres, which are often observed with a lower signal-to-noise ratio.

Recently, we observed a high-resolution spectrum of a T6.5-type brown dwarf Gl 229B with the InfraRed Doppler (IRD, R ~ 70,000) spectrograph mounted on the Subaru Telescope. We have constrained its atmospheric properties, such as the molecular abundances and thermal structure, using an inverse-problem approach with ExoJAX. ExoJAX is an auto-differentiable high-resolution spectrum model for exoplanets and brown dwarfs we recently developed (Kawahara, Kawashima et al. 2022). In addition, we have revealed that in some wavelength regions, specific molecular line lists do not match the observed absorption features.