[P-AE18] Exoplanets

[PAE18-15] Validation of an Eccentric Hot Jupiter Transiting the Edge of a Mid-A-type star TOI-1355

*Noriharu Watanabe¹, Norio Narita^1,2, Akihiko Fukui¹, Bun'ei Sato³, Keisuke Isogai^1,4, John Livingston^2,5, Jerome de Leon¹, Yugo Kawai¹, Masashi Omiya^2,5, Hideyuki Izumiura⁵, Akito Tajitsu⁵, Nobuhiko Kusakabe^2,5, Motohide Tamura^1,2,5 (1.The University of Tokyo, 2.Astrobiology Center, 3.Institute of Science Tokyo, 4.Kyoto University, 5.The National Astronomical Observatory of Japan)

Keywords:Exoplanet, Hot star, Hot Jupiter

Hot Jupiter, a gas giant orbiting with a short period of less than 10 days, is a difficult planet to form in situ. Thus, some orbital evolution models have been proposed, such as the disk migration and the high eccentricity migration. The disk migration involves a gas giant dropping near its host star through disk-planet interaction and aligning the orbit with the stellar spin. In contrast, the high eccentricity migration is a model in which a gas giant with a high eccentric and misaligned orbit approaches its host star due to the circularization from the tides of planetary deformation. High eccentricities and misalignments can arise from interactions with other giant planets or outer companions. Because a hot star, whose effective temperature is above 7000K, has no convective zones in its envelopes and hardly undergoes realignment, the system with a hot Jupiter and a hot star is favorable to research orbital evolution.

In this study, we discovered a massive hot Jupiter around TOI-1355, one of the A-type stars, from the TESS transit survey, and the follow-up observations such as the high-resolution spectrograph Seimei/GAOES-RV and the multi-band camera LOCGT(2m)/MuSCAT3. This is the first discovery of an eccentric hot Jupiter around a hot star, which suggests that this hot Jupiter has undergone the high eccentricity migration. We also detected the nodal precession, a phenomenon that the orbital axis precesses relative to the stellar rotational axis, by measuring the change in its impact parameter (an apparent distance between the transit trajectory and the center of the host star). This implies that the orbital axis is almost perpendicular to the stellar rotational axis and we cannot observe its transit since 2028 CE.