Planet のバックアップ(No.75)

惑星セミナー2021 †

惑星セミナーは原則として毎週木曜日の15:00から開催しています。（連絡係：星野遥, 荒川創太, 高橋実道，古家健次）
astro-phセミナーは毎週月曜日の12:00から開催しています。（連絡係：Carol Kwok，瀧哲朗）

Schedule & History †

2020年度 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 4/15 15:00-	All members	Self-introduction		古家
前期第2回 4/22 15:00-	All members	Self-introduction		古家
前期第3回 5/13 14:00-	Teruyuki Hirano (ABC)	Near Infrared Spectroscopy as a Powerful Tool to Probe Exoplanetary Systems	14:00	古家
前期第4回 5/20 15:00-	Ryuki Hyodo (ISAS/JAXA)	Planetesimal formation -- Around the snow line and the "no-drift" mechanism		荒川
前期第5回 6/17 15:00-	Riouhei Nakatani (RIKEN)	Photoevaporation of Protoplanetary Disks: Revisiting the Underlying Physics and the Gravitational Radius		高橋
前期第XX回 6/24 15:00-	Hiroaki Kaneko (titech)			星野

5/20 Ryuki Hyodo (ISAS/JAXA), Planetesimal formation -- Around the snow line and the "no-drift" mechanism: Forming planetesimals in protoplanetary disks is a major challenge in our current understanding of planet formation. Icy pebbles mixed with silicate dust formed at the outer disk drift inward due to the gas drag. We performed 1D diffusion-advection simulations that include the back-reaction (the inertia) to radial drift and diffusion of icy pebbles and silicate dust, ice sublimation, the release of silicate dust, and their recycling through the recondensation and sticking onto pebbles outside the snow line. In this talk, I will present how icy pebbles and silicate dust pile up around the snow line. I also report a new mechanism, the “no-drift” runaway pile-up, that leads to a runaway accumulation of pebbles in disks, thus favoring the formation of planetesimals by streaming and/or gravitational instabilities. References: Hyodo et al. 2021 A&A, 646, A14; Ida et al. 2021 A&A, 646, A13; Hyodo et al. 2021 A&A, 645, L9

6/17 Riouhei Nakatani (RIKEN), Photoevaporation of Protoplanetary Disks: Revisiting the Underlying Physics and the Gravitational Radius: In a variety of astrophysical problems, we find a situation where a clump of gas is irradiated by ultraviolet and X-ray from radiation sources. An important outcome of this process is that excessive photon energy goes into the heat for the gas, which results in driving winds. This wind-driving process, termed photoevaporation, is essential to determine the fate of the irradiated objects. Protoplanetary disks are one of such objects. The stellar UV and X-ray can yield sufficiently high mass-loss rates that can disperse the disks within 10 Myr. The gravitational radius is often used as a criterial radius above which the photoheated gas is possible to escape from the gravitational binding of the host star. However, the gravitational radius is derived from dimensional analysis and thus does not provide a definite criterion regarding the escape capability. We have recently developed an analytic model for photoevaporation in a first-principles approach. It is of use to understand the basic physics operating in the vicinity of the wind-launching points. Our model naturally sets a gravitational-radius-like criterion, which is fundamentally different from the gravitational radius in origin. In this talk, I first present the analytic model. Then, the model aside, I introduce our recent numerical works regarding photoevaporation of protoplanetary disks hosted by intermediate-mass stars.