高温の恒星周辺を楕円軌道で公転するホットジュピターを発見 ──トランジット観測のタイムリミットはあと7年──

2026-09-18 東京大学

地球から見たTOI-1355bの軌道のイメージ。楕円軌道のため、恒星が軌道の中心からやや離れています。
2026年の時点では、恒星の縁をかすめるような軌道に見えます。

＜関連情報＞

• https://www.c.u-tokyo.ac.jp/info/news/topics/20260918140000.html
• https://academic.oup.com/pasj/advance-article/doi/10.1093/pasj/psag103/8792826

初期A型星TOI-1355のトランジット軌道から離脱する、偏心軌道を持つ高温のスーパージュピターの発見 Discovery of an eccentric hot super-jupiter leaving the transiting geometry of the early-A-type star TOI-1355

Noriharu Watanabe, Norio Narita, Akihiko Fukui, Bun’ei Sato, Keisuke Isogai, John H Livingston, Jerome P de Leon, Daniel Huber, Yugo Kawai, Yuya Hayashi,…
Publications of the Astronomical Society of Japan  Published:18 September 2026
DOI:https://doi.org/10.1093/pasj/psag103

Abstract

Hot Jupiters orbiting hot stars (T_eff＞70000⁠ K) are suggested to have experienced high-eccentricity migration, often evidenced by the tendency for misaligned orbits, despite their circular orbits. In this paper, we present the discovery of TOI-1355 b: an eccentric (e～0.22⁠⁠) hot Jupiter with a mass of m_p～5.8M_J and a radius of R_p～1.4R_J orbiting an A-type star with a period of about 2.17 d, identified from the TESS transit survey and subsequent follow-up observations. We measured the stellar parameters using the data from the high-resolution spectrograph Seimei/GAOES-RV and obtained the planetary parameters from the photometric data acquired by TESS and ground-based telescopes. This is one of the rare eccentric hot Jupiters around hot stars. This system could be undergoing high-eccentricity migration. We detected nodal precession by measuring the change in its impact parameter. This implies that its transit will no longer be observable from the middle of 2033. Nevertheless, TOI-1355 b is anticipated to be a compelling target for future atmospheric observations, given the hint of atmospheric variability detected in this study.