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Planet のバックアップ(No.115)


惑星セミナー2020

惑星セミナーは原則として毎週木曜日の14:00から開催しています。(連絡係:星野 遥, 荒川 創太, 古家 健次, 荻原 正博)
astro-phセミナーは毎週金曜日の12:00から開催しています。(連絡係:Carol Kwok)

Schedule & History

2019年度 2018年度 2017年度 2016年度 2015年度 2014年度

日程発表タイトルRemarks担当
前期 第1回 4/9 15:00-All membersSelf-introduction15:00荻原
前期 第2回 4/16 14:00-Haruka Hoshino, Hirotaka HohokabeSmall ASJ meeting荒川
前期 第3回 4/23 14:00-Yuki Yoshida, Eiichiro KokuboSmall ASJ meeting星野
前期 第4回 5/14 14:00-Sota ArakawaThermal history and tidal evolution of trans-Neptunian satellite systems古家
前期 第5回 5/28 14:00-Takuya Takarada (ABC)Radial-velocity search and statistical studies for short-period planets in the Pleiades open cluster荒川
前期 第6回 6/4 16:00-Beibei Liu (Lund Univ)Pebble-driven planet formation around very low-mass stars and brown dwarfs16:00荻原
前期 第7回 7/9 14:00-Yuka Fujii星野
6/4 Beibei Liu, Pebble-driven planet formation around very low-mass stars and brown dwarfs
We conduct a pebble-driven planet population synthesis study to investigate the formation of planets around very low-mass stars and brown dwarfs, in the (sub)stellar mass range between 0.01 M⊙ and 0.1 M⊙. Based on the extrapolation of numerical simulations of planetesimal formation by the streaming instability, we obtain the characteristic mass of the planetesimals and the initial masses of the protoplanets (largest bodies from the planetesimal size distributions), in either the early self-gravitating phase or the later non-self-gravitating phase of the protoplanetary disk evolution. We find that the initial protoplanets form with masses that increase with host mass, orbital distance and decrease with disk age. Around late M-dwarfs of 0.1 M⊙, these protoplanets can grow up to Earth-mass planets by pebble accretion. However, around brown dwarfs of 0.01 M⊙, planets do not grow larger than Mars mass when the initial protoplanets are born early in self-gravitating disks, and their growth stalls at around 0.01 Earth-mass when they are born late in non-self-gravitating disks. Around these low mass stars and brown dwarfs, we find no channel for gas giant planet formation because the solid cores remain too small. When the initial protoplanets form only at the water-ice line, the final planets typically have ≳15% water mass fraction. Alternatively, when the initial protoplanets form log-uniformly distributed over the entire protoplanetary disk, the final planets are either very water-rich (water mass fraction ≳15%) or entirely rocky (water mass fraction ≲5%).