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Planet のバックアップ差分(No.76)

  • 追加された行はこの色です。
  • 削除された行はこの色です。
* 惑星セミナー2019 [#zbb5ecca]

惑星セミナーは原則として毎週金曜日の15:00から理論部セミナー室で開催しています。(連絡係:荻原 正博)~
astro-phセミナーは毎週金曜日の12:00から理論部セミナー室で開催しています。(連絡係:Carol Kwok)

// セミナー発表順番

** Schedule & History [#vfafd1d8]


|[[前期 第1回 4/11 14:30->#planet0411]]|Shinsuke Takasao| 3D MHD simulations of Inner Protoplanetary Disks |14:30|
|[[前期 第2回 4/18 14:00->#planet0418]]|Carina Heinreichsberger (Universität Wien)|Terrestrial or Gaseous? A classification of exoplanets according to density, mass and radius||
|[[前期 第3回 4/25 14:00->#planet0425]]|Kazunari Iwasaki |Chemistry in Debris Disks ||
|[[前期 第4回 5/16 14:30->#planet0516]]|Yuhito Shibaike (Tokyo Tech) |A new formation scenario for the Galilean satellites |14:30|
|[[前期 第5回 5/23 15:30->#planet0523]]|Yuji Matsumoto (ASIAA) |The orbital stability of planets in resonances considering the evolution of mass ratio |15:30|
//6/6: 小久保さん集中講義
|[[前期 第6回 6/13 15:00->#planet0613]]|Hiroaki Kaneko (Tokyo Tech) |ストリーミング不安定の発生機構の物理的解釈 |In Japanese 15:00|
|[[前期 第7回 6/20 14:00->#planet0620]]|Yuhiko Aoyama (University of Tokyo) |Theoretical modeling of hydrogen line emission from accreting gas giants: How gas flows around LkCa15b and PDS70b ||
|[[前期 第8回 6/27 15:00->#planet0627]]|Shoji Mori (University of Tokyo) |Inefficient Magnetic Accretion Heating in Protoplanetary Disks |15:00|
|[[前期 第9回 7/19 14:00->#planet0719]]|Takaya Nozawa| On the condensation of dust in the pre-solar nebula |Friday|
|[[前期 第10回 8/1 14:00->#planet0801]]|Ryosuke Tominaga (Nagoya University)| On the growth of secular instabilities triggered by dissipation in protoplanetary disks ||
|[[後期 第1回 10/11 15:00->#planet1011]]|Aya Higuchi (NAOJ)| Toward understanding origin of gas in debris disks ||
//6/27は15時以降に(吉田君セミナーあり): Fukui
//7/4, 7/11→小久保さん休み
//7/25: Carol

//杉浦さん, Tominagaさん

// ←ダブルスラッシュはコメントアウト
//:&aname(planet0418){4/18}; Dimitri Veras, The growing field of post-main-sequence exoplanetary science, with strong connections to the solar system|
//The quest for identifying the bulk chemical composition of extrasolar planets and robust observational evidence that between 25% and 50% of all Milky Way white dwarfs host currently dynamically-active planetary systems motivate investigations that link their formation and fate. Here I provide a review of our current knowledge of these systems, including an update on the observational and theoretical aspects of the groundbreaking discovery of at least one disintegrating minor planet transiting white dwarf WD 1145+017. I show how this field incorporates several facets of solar system physics and chemistry, and how its interdisciplinary nature requires input from orbital dynamics, stellar evolution, astrochemistry, atmospheric science and surface processes.


//:&aname(planet1107){5/21}; 名前 タイトル|

:&aname(planet0418){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.

:&aname(planet0516){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 Jupiter’s 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.

:&aname(planet0613){6/13}; Hiroaki Kaneko, ストリーミング不安定の発生機構の物理的解釈|
Youdin & Goodman (2005)(YG05)が発見したダスト・ガスの二流体の線形不安定 “Streaming Instability” (SI)によるダスト密度上昇とそれに続く自己重力崩壊が微惑星形成の一つの可能性として考えられている。SIについては線形および非線形の数値計算がされていて不安定が存在することは確かであるものの、メカニズムははっきりしていない。今回は各物理量の摂動の位相差に注目して、ガスが支配的な場合におけるSIのメカニズムを提案する。それは以下の通りである。
1. 基本場としてガスはダストから角運動量を受け取り、中心星より遠方へと運動する。ダスト密度に濃淡があるとすると、ダスト密度の違いによってガスへの角運動量の供給に違いが生じ、半径方向にガス圧力の摂動ができる。
2. 高圧部からは鉛直方向にガスが流出し、低圧部にはガスが流入する。ダストもこれに引きずられ、同様に高圧部から流出、低圧部に流入する。
3. ガスが支配的な状態ではダスト密度の摂動の位相は中心星方向に進む。ダスト密度の極大はガスの低圧部へと向かい、そこで鉛直方向から流入するダストと合流し、ダスト密度の摂動の振幅が大きくなる。

:&aname(planet0620){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 Hα. Hydrogen line emission such as Hα 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 Hα. The physical mechanism for the Hα 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 Hα 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 Hα at significant intensity. Comparing our theoretical Hα 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 Hα emission. From this, gas flow around the two gas giants is discussed.

:&aname(planet0627){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.

:&aname(planet0801){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.

:&aname(planet0111){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, β 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 μm dust continuum emission observed with ALMA.