[P-EM11] 系外惑星

[PEM11-P03] Oxygen airglow of Earth-like exoplanets around active low-mass stars

*中山 陽史¹、川内 紀代恵²、亀田 真吾¹、寺田 直樹³、生駒 大洋⁴ (1.立教大学、2.東京大学、3.東北大学、4.国立天文台)

キーワード：系外地球型惑星、熱圏、トランジット観測

Understanding the atmosphere of terrestrial exoplanets in the habitable zone around low-mass stars is an important issue for planetary science and astronomy. Although JWST would bring us a new era of characterizations of the atmosphere, detecting oxygen features in Earth-like planets needs unrealistic observation times. On the other hand, high-dispersion spectroscopy is a powerful tool for detecting line features. It has already achieved success in characterizing extended atmospheres of hot Jupiters. Recently, our new estimates of the thermospheric structure of Earth-like planets show upper atmosphere is mainly cooled by oxygen lines at 630nm when planets receive high XUV flux which is appropriate for low-mass star systems. Thus it has great potential as a new tool for characterizing terrestrial atmospheres.

We estimate line emission profiles of atomic oxygen for different XUV conditions and planetary mass. We adopt the temperature and compositional profiles estimated by our thermospheric model for the Earth-like lower boundary conditions (Nakayama et al. 2022). We find emission signals are about 100 times larger than the atmospheric absorption signals in the primary transit and up to 10% of stellar flux. Because line features are resolved by ground telescopes with typical high-dispersion spectrometers, we propose oxygen airglow of terrestrial exoplanets as a good candidate for characterizing terrestrial atmospheres.