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Last-modified: 2019-10-10 () 11:24:09 (4d)
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astro-phߥʡ轵12:00ߥʡdzŤƤޤϢCarol Kwok

Schedule & History

2018ǯ 2017ǯ 2016ǯ 2015ǯ 2014ǯ

1 4/11 14:30-Shinsuke Takasao3D MHD simulations of Inner Protoplanetary Disks14:30
2 4/18 14:00-Carina Heinreichsberger (Universität Wien)Terrestrial or Gaseous? A classification of exoplanets according to density, mass and radius
3 4/25 14:00-Kazunari IwasakiChemistry in Debris Disks
4 5/16 14:30-Yuhito Shibaike (Tokyo Tech)A new formation scenario for the Galilean satellites14:30
5 5/23 15:30-Yuji Matsumoto (ASIAA)The orbital stability of planets in resonances considering the evolution of mass ratio15:30
6 6/13 15:00-Hiroaki Kaneko (Tokyo Tech)ȥ꡼ߥ԰ȯʪŪIn Japanese 15:00
7 6/20 14:00-Yuhiko Aoyama (University of Tokyo)Theoretical modeling of hydrogen line emission from accreting gas giants: How gas flows around LkCa15b and PDS70b
8 6/27 15:00-Shoji Mori (University of Tokyo)Inefficient Magnetic Accretion Heating in Protoplanetary Disks15:00
9 7/19 14:00-Takaya NozawaOn the condensation of dust in the pre-solar nebulaFriday
10 8/1 14:00-Ryosuke Tominaga (Nagoya University)On the growth of secular instabilities triggered by dissipation in protoplanetary disks
1 10/11 15:00-Aya Higuchi (NAOJ)Toward understanding origin of gas in debris disks
4/18 Carina Heinreichsberger, Terrestrial or Gaseous? A classification of exoplanets according to density, mass and radius
When looking at Exoplanet Archives the class of a planet is not given. Therefore I tried to find an easy and fast way to classify exoplanets using only density, mass and radius. In this talk I will discuss the formation theory of Planets to explain the boundaries between the different classes (gas, terrestrial) and show the results of my empirical study.
5/16 Yuhito Shibaike, A new formation scenario for the Galilean satellites
It is generally accepted that the four major (Galilean) satellites formed out of the gas disk that accompanied Jupiters formation. I will discuss a new formation scenario for the Galilean satellites, based on the capture of several planetesimal seeds and subsequent slow accretion of pebbles. Our slow-pebble-accretion scenario can reproduce the following characteristics: (1) the mass of all the Galilean satellites; (2) the orbits of Io, Europa, and Ganymede captured in mutual 2:1 mean motion resonances; (3) the ice mass fractions of all the Galilean satellites; (4) the unique ice-rock partially differentiated Callisto and the complete differentiation of the other satellites.
6/13 Hiroaki Kaneko, ȥ꡼ߥ԰ȯʪŪ
Youdin & Goodman (2005)(YG05)ȯȡήΤ԰ Streaming Instability (SI)ˤ̩پ徺Ȥ³ʽΰĤβǽȤƹͤƤ롣SIˤĤƤοͷ׻Ƥ԰꤬¸ߤ뤳ȤϳΤǤΤΡᥫ˥ϤϤäꤷƤʤϳʪ̤ưΰ꺹ܤơŪʾˤSIΥᥫ˥Ƥ롣ϰʲ̤Ǥ롣 1. ܾȤƥϥȤѱư̤ꡢ濴ؤȱư롣̩٤ǻøȤȡ̩٤ΰ㤤ˤäƥؤγѱư̤ζ˰㤤Ⱦ˥ϤưǤ롣 2. ⰵϱľ˥ήФ㰵ˤϥή롣Ȥ⤳˰졢Ʊͤ˹ⰵήС㰵ή롣 3. Ūʾ֤Ǥϥ̩٤ưΰ濴˿ʤࡣ̩٤ζϥ㰵ؤȸDZľήȤȹή̩٤ưο礭ʤ롣
6/20 Yuhiko Aoyama, Theoretical modeling of hydrogen line emission from accreting gas giants: How gas flows around LkCa15b and PDS70b
Observation of growing protoplanets is key to understand planet formation. Planets are thought to form in the gaseous disk around pre-main-sequence stars, so-called proto-planetary disk. So far, a few planets embedded in such disks are detected. Among them, LkCa15b and PDS70b are particularly interesting planets. These planets are reported to be bright not only in the infra-red but also in H. Hydrogen line emission such as H needs hot hydrogen gas with a temperature higher than ~104 K as their source. Such a high temperature is unlikely to be realized in the protoplanet nor circum-planetary disk. Also, observationally, other wavelengths observations suggest a few thousand K of gas temperature, which is too cool to emit observable H. The physical mechanism for the H emission is poorly understood in planet formation context. In this study, we focus on two accreting flows. One flows from a proto-planetary disk to a circum-planetary disk. According to recent 3D hydrodynamic simulations, the accreting gas almost vertically onto and collides with the surface of the circumplanetary disk at a super-sonic velocity. And the other flow comes from circum-planetary disks to a planetary surface. In stellar accretion context, both theoretical model and observational data suggest surrounding gaseous disk is truncated around the central object and gas falls from the disk to the object with a supersonic velocity, when the object has a strong magnetic field. In both cases, the gas passes through a strong shock wave and gets hot enough to emit hydrogen lines. However, the gas instantly cools. So we have to study whether the shock-heated gas can emit significant H faster than the cooling. Here, we have developed a 1D radiative hydrodynamic model of the flow after the shock with detailed calculations of chemical reactions and electron transitions in hydrogen atoms. Then, we quantify the hydrogen line emission from the shock surface. Our model concluded the shock-heated gas can emit H at significant intensity. Comparing our theoretical H intensity with the observed ones from LkCa15b and PDS70b, most of the gas going to the planet have to pass through a strong shock and contribute to H emission. From this, gas flow around the two gas giants is discussed.
6/27 Shoji Mori, Inefficient Magnetic Accretion Heating in Protoplanetary Disks
The gas temperature in the inner region of protoplanetary disks is thought to be determined by accretion heating, which is conventionally attributed to turbulent dissipation. However, recent studies have suggested that the inner disk (a few AU) is largely laminar, with accretion primarily driven by magnetized disk winds, as a result of nonideal magnetohydrodynamic (MHD) effects from weakly ionized gas, suggesting an alternative heating mechanism by Joule dissipation. We perform local stratified MHD simulations including all three non-ideal MHD effects (Ohmic, Hall, and ambipolar diffusion), and investigate the role of Joule heating and the resulting disk vertical temperature profiles. We find that in the inner disk, as Ohmic and ambipolar diffusion strongly suppress electrical current around the midplane, Joule heating primarily occurs at several scale heights above the midplane, making midplane temperature much lower than that with the conventional viscous heating model. Including the Hall effect, Joule heating is enhanced/reduced when magnetic fields threading the disks are aligned/anti-aligned with the disk rotation, but is overall ineffective. Our results suggest that the midplane temperature in the inner PPDs is almost entirely determined by irradiation heating. We will also discuss the evolution of the water snow line based on our results and the formation process of the Earth.
8/1 Ryosuke Tominaga, On the growth of secular instabilities triggered by dissipation in protoplanetary disks
Understanding structures of protoplanetary disks and its evolution is the key to reveal the planet formation. Recent observations with ALMA have found that many disks have rings and gaps in the spatial distribution of dust grains. These annular substructures are thought to be related to the planet formation, but its origin is still under debate. One of the possible mechanisms for creating the observed substructures is the ring/gap formation via two secular instabilities (Takahashi & Inutsuka 2016; Tominaga et al. 2019). One of those is called secular gravitational instability (GI), which grows by friction between dust and gas. The other is two-component viscous gravitational instability (TVGI) that we newly found. TVGI is a secular instability triggered by a combination of friction and turbulent viscosity. Performing a linear analysis, we find that the growth of those secular instabilities can be understood from the point of view of destabilization of a static mode that is a steady solution of the linearized perturbation equations. We have also been working on the non-linear evolution by performing numerical simulations. The results show that rings formed via the linear growth of the instabilities collapse self-gravitationally at the non-linearly evolutionary stage. The surface density of the dust is found to become about 10 times higher than the unperturbed value.
10/11 Aya Higuchi, Toward understanding origin of gas in debris disks
Debris disks have optically thin dust components around main-sequence stars. Recently, several debris disks harboring a gas component have been discovered in survey observations at optical, infrared, and radio wavelengths, and its origin has been discussed in terms of the evolution of protoplanetary disks and the formation of planetary bodies. In fact, many debris disks are known to reveal submillimeter-wave CO emission, e.g., 49 Ceti, Pictoris, and 15 others or more. In addition to the CO emission, the submillimeter-wave [C I] emission has been observed toward a few debris disks. I will present recent observations of gaseous debris disks and also present our result of the first subarcsecond images of 49 Ceti in the [C I] 3P1–3P0 emission and the 614 m dust continuum emission observed with ALMA.