Understanding the Mass-Loss Mechanism of Close-in Exoplanets by Observations of Low-Mass Stars

2023 Fiscal Year Final Research Report

• Project/Area Number: 19K14783
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 17010:Space and planetary sciences-related
• Research Institution: National Institutes of Natural Sciences (2020-2023); Tokyo Institute of Technology (2019)
• Principal Investigator: Hirano Teruyuki 大学共同利用機関法人自然科学研究機構(機構直轄研究施設), アストロバイオロジーセンター, 准教授 (10727449)
• Project Period (FY): 2019-04-01 – 2024-03-31
• Keywords: 太陽系外惑星 / 低温度星 / トランジット惑星 / 惑星大気散逸 / 近赤外線高分散分光観測

Outline of Final Research Achievements

With a goal of unveiling the origin of the observed distributions of exoplanets, such as the lack of super-Earths (so-called the "radius gap"), we conducted the search and characterization of exoplanets around low-mass stars (i.e., M dwarfs), which were relatively unexplored in the past. Focusing on (A) development of the radial-velocity technique in the near infrared, and (B) the validation and confirmation of transiting planets around low-mass stars, we studied various aspects of exoplanets around low-mass stars. In WP (A), we found we can achieve a radial-velocity precision of ~2m/s in the near infrared by establishing a data analysis technique that takes into account the telluric absorption lines. For WP (B), we validated and confirmed dozens of small planets around low-mass stars, including an Earth-sized planet at 22 pc and two ultra-short-period planets around mid-M dwarfs. Those planets are important targets for future atmospheric characterizations.

Free Research Field

太陽系外惑星科学，光赤外天文学

Academic Significance and Societal Importance of the Research Achievements

太陽系外惑星系の多様性および分布の起源には未だ多くの謎があり，多様な系外惑星系の観測によりその特徴を明らかにすることでその成因に迫ることができる。本研究は，近赤外線での精密視線速度測定法を開発することで低温度星周りの惑星の発見と特徴付けを可能にする観測的基盤を整備した。さらに，低温度星周りのトランジット惑星の発見を通じて，太陽型星周りの惑星の特徴との類似点・相違点が徐々に明らかになった。こうした観測結果は今後惑星系の形成・進化のメカニズムを詳細に明らかにする上で貴重な制約となると考えられる。