Planet のバックアップ(No.59)

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 members	Self-introduction	15:00	荻原
前期第2回 4/16 14:00-	Haruka Hoshino, Hirotaka Hohokabe	Small ASJ meeting		荒川
前期第3回 4/23 14:00-	Yuki Yoshida, Eiichiro Kokubo	Small ASJ meeting		星野
前期第4回 5/14 14:00-	Sota Arakawa	Thermal 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 dwarfs	16:00	荻原
前期第7回 7/9 14:00-	Yuka Fujii	Detecting molecular lines of warm/temperate exoplanets with mid-infrared high-resolution spectroscopy		星野
前期第8回 7/21 14:00-	Masato Ishizuka (U. Tokyo)	Studies of exoplanets with high resolution spectroscopy		古家
後期第1回 10/16 14:00-	Makiko Ban	Free-floating planet research and perspective		荻原
後期第2回 10/30 14:30-	Yuki Tanaka (Tohoku Univ.)	Gap formation by a super-Jupiter-mass planet and its effects on the planetary mass accretion rate	14:30	荻原

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%).

10/16 Makiko Ban, Free-floating planet research and perspective: The free-floating planet (FFP) is a unique type of exoplanet. There have been very scarce discoveries about it because of the difficulty of observation. The up-comming space-based telescope missions (Euclid and Roman) are expected to boost the FFP research. Here, I'd like to introduce FFPs, the challenges about the research we are facing, and future perspectives that will be offered by those up-comming missions through my latest paper.

10/30 Yuki Tanaka, Gap formation by a super-Jupiter-mass planet and its effects on the planetary mass accretion rate: A giant planet embedded in a protoplanetary disk creates a gap structure along with its orbit by disk-planet interaction. Physical properties of the gap depend on several conditions such as mass of the planet and disk structures, and they affect both mass accretion rate onto the planet via the gap and migration rate of the planet. Therefore, the properties of the gap are important to investigate formation and evolution of planetary systems. Recently, numerical simulations of the disk-planet interaction have been done intensively, and the disk properties such as width and depth of the gap, and mass accretion rate have been studied. However, previous studies mainly focused on planets less massive than Jupiter. In addition, there are a discrepancy between several previous works on the mass accretion rate onto the planet heavier than Jupiter. Since a lot of super-Jupiter-mass planets have been found, formation and evolution of them in the protoplanetary disk should be investigated in more detail. We performed a set of hydrodynamic simulation of disk-planet interaction and investigated the properties of the gap and their parameter dependence. We varied the planetary mass from 1 to 10 Jupiter masses. We found that the gap becomes deeper as planet's mass increases up to around 3 Jupiter masses, but in more massive cases the outer edge of the gap shows significant eccentricity, which is consistent with several previous works. In this eccentric regime, the gap depth becomes shallower than an empirical relation between the depth and the planetary mass due to non-steady behavior of the gap outer edge. We also estimated the mass accretion rate onto the planet by using our result and found that the accretion rate can increase when the planet's mass is heavier because of the eccentricity of the gap.