International joint research for maser variability and mass accretion processes in high-mass protostars

2021 Fiscal Year Final Research Report

• Project/Area Number: 17K05398
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Astronomy
• Research Institution: National Astronomical Observatory of Japan
• Principal Investigator: Hirota Tomoya 国立天文台, 水沢VLBI観測所, 助教 (10325764)
• Project Period (FY): 2017-04-01 – 2022-03-31
• Keywords: 電波天文学 / 大質量星形成 / メーザー / 超長基線電波干渉計(VLBI) / アルマ / タイムドメイン天文学 / 多波長天文学

Outline of Final Research Achievements

This research aims to investigate time variation of strong maser emission associated with high-mass protostars, which are newly born stars more massive than 8 times the Solar masses, through radio interferometer observations. In the first year of this study, an international collaboration team Maser Monitoring Organization (M2O) was established during an international conference in Italy. As a result, maser flares in two sources, G358.93 and G24.33, were successfully identified. In addition, detailed observational studies on well studied sources, NGC6334 and S255, were also carried out. It is found that the maser flare could be caused by luminosity increase due to mass accretion onto protostars, and that the accretion rate and timescale show source-to-source differences.

Free Research Field

電波天文学

Academic Significance and Societal Importance of the Research Achievements

大質量星は、星団で形成され周囲のガスを電離したり、進化末期に超新星爆発を起こして重元素を放出したりするなど宇宙や銀河の進化にも大きな影響を与える重要な存在である。しかし、生まれたばかりの大質量原始星は数が少ないために、これらがどのようにして周囲から物質を獲得（質量降着）して成長するのか、という基本問題についても理解が進んでいない。本科研費による国際共同研究は、大質量原始星が成長する際に起こる周辺環境の変化をメーザー放射の時間変動によって捉える手法を確立し、大質量星形成の理論を構築する上で重要な役割を果たしている。