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Planet のバックアップの現在との差分(No.99)


  • 追加された行はこの色です。
  • 削除された行はこの色です。
#norelated
* 惑星セミナー2019 [#zbb5ecca]
* 惑星セミナー2020 [#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)
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)

// セミナー発表順番
// 

** Schedule & History [#vfafd1d8]

[[2019年度>Planet2019]]
[[2018年度>Planet2018]]
[[2017年度>Planet2017]]
[[2016年度>Planet2016]]
[[2015年度>Planet2015]]
[[2014年度>Planet2014]]

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|日程|発表|タイトル|Remarks|h
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//|BGCOLOR(#ddf):|BGCOLOR(#ffd):|BGCOLOR(#ffd):|c
|[[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 ||
|[[後期 第2回 11/18 14:00->#planet1118]]|Alessandro Trani| TSUNAMI: a fast and accurate few-body code for planetary dynamics including tidal forces ||
|[[後期 第3回 1/16 16:00->#planet0116]]|Kazunari Iwasaki| Global Non-ideal MHD Simulations of Protoplanetary Disks |16:00|
|[[後期 第4回  >#planet0127]]|Haruka Hoshino| 巨大衝突によって形成される惑星系の軌道構造の中心星質量依存性  |practice|
|[[後期 第5回 2/4 15:00->#planet0204]]|Akihiko Fukui (University of Tokyo)| 重力マイクロレンズ系外惑星探索の現状と展望 |Tuesday|
|[[後期 第6回 2/27 15:00->#planet0227]]|Masanobu Kunitomo (Kurume University)| Coevolution of a star and planets in the pre- and post-main-sequence phases ||
|[[後期 第7回 3/5 15:00->#planet0305]]|Kenji Kurosaki (Nagoya University)| Giant impact on ice giants in the proto-planetary disk ||
|[[後期 第8回 3/9 15:00->#planet0309]]|Kazumasa Ohno (Tokyo Tech)| TBA |Monday|
|BGCOLOR(#ccf):|BGCOLOR(#ffc):|BGCOLOR(#ffc):|BGCOLOR(#fcf):|BGCOLOR(#cff):|c
|日程|発表|タイトル|Remarks|担当|h
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//|BGCOLOR(#ddf):|BGCOLOR(#ffd):|BGCOLOR(#ffd):|BGCOLOR(#cff):|c
|[[前期 第1回 4/9 15:00->#planet0409]]|All members| Self-introduction |15:00|荻原|
|[[前期 第2回 4/16 14:00->#planet0409]]|Haruka Hoshino, Hirotaka Hohokabe| Small ASJ meeting ||荒川|
|[[前期 第3回 4/23 14:00->#planet0409]]|Yuki Yoshida, Eiichiro Kokubo| Small ASJ meeting ||星野|
|[[前期 第4回 5/14 14:00->#planet0409]]|Sota Arakawa| Thermal history and tidal evolution of trans-Neptunian satellite systems ||古家|
|[[前期 第5回 5/28 14:00->#planet0528]]|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->#planet0606]]|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->#planet0606]]|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->#planet0606]]|Masato Ishizuka (U. Tokyo)|Studies of exoplanets with high resolution spectroscopy||古家|
|[[後期 第1回 10/16 14:00->#planet1016]]|Makiko Ban|Free-floating planet research and perspective||荻原|
|[[後期 第2回 10/30 14:30->#planet1030]]|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|
|[[後期 第3回 11/20 14:00->#planet1031]]|Shota Notsu (RIKEN)| The composition of hot Jupiter atmospheres assembled within chemically evolved protoplanetary discs||古家|
|[[後期 第4回 11/27 14:00->#planet1127]]|Kazuaki A. Homma (Tokyo Tech)| Vertical growth of dust particles with UV-irradiation and organic-synthesis in protoplanetary disks||荒川|

//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
//7/18→7/19
//7/25: Carol
//8/1

//今後の予定
//Nov 25 2pm, 野村不可
//Dec 9  2pm, 
//Dec 16 2pm, 荻原不可
//Dec 23 2pm, 小久保△
//
//今後の候補
//國友、石澤、鈴木ISAS、福井
//野村さんのコロキウムで聞けなかった部分(実際にやっている学生でも)
//
//鈴木さん(ISAS)
//杉浦さん, Tominagaさん
//内部:小久保、押野、荻原、波々伯部、Carol、星野
//原川さん、森島さん、森さん(東工大)
//小久保さん:Ishigakiさん(ISAS)
//荻原:駒木さん(東大), Sakurabaさん(東工大), Liu(Lund)
//荒川:本間和明さん (D1), 長谷川幸彦さん (東大駒場)
//古家:Gianni Cataldi(東大天文),野津翔太さん(理研) 
//石澤さん(京大)
//森島さん


// ←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.

//アブスト

//:&aname(planet1107){5/21}; 名前 タイトル|
//アブスト

:&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(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(planet0604){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%).

:&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(planet1016){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.

:&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(planet1030){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.

:&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(planet1031){11/20}; Shota Notsu, The composition of hot Jupiter atmospheres assembled within chemically evolved protoplanetary discs|
The radial-dependent positions of snowlines of abundant oxygen- and 
carbon-bearing molecules in protoplanetary discs will result in systematic
radial variations in the C/O ratios in the gas and ice. 
This variation is proposed as a tracer of the formation location of gas-giant planets. 
However, disc chemistry can affect the C/O ratios in the gas and ice, thus potentially
erasing the chemical fingerprint of snowlines in gas-giant atmospheres.
We calculate the molecular composition of hot Jupiter atmospheres using elemental
abundances extracted from a chemical kinetics model of a disc midplane where we 
have varied the initial abundances and ionization rates. The models predict a
wider diversity of possible atmospheres than those predicted using elemental
ratios from snowlines only. As found in previous work, as the C/O ratio exceeds
the solar value, the mixing ratio of CH4 increases in the lower
atmosphere, and those of C2H2 and HCN increase mainly in the upper
atmosphere. The mixing ratio of H2O correspondingly decreases. We find
that hot Jupiters with C/O>1 can only form between the CO2 and CH4
snowlines. Moreover, they can only form in a disc which has fully inherited
interstellar abundances, and where negligible chemistry has occurred. Hence,
carbon-rich planets are likely rare, unless efficient transport of
hydrocarbon-rich ices via pebble drift to within the CH4 snowline is a
common phenomenon. We predict combinations of C/O ratios and elemental
abundances that can constrain gas-giant planet formation locations relative to
snowline positions, and that can provide insight into the disc chemical
history. 
This seminar talk is mainly based on our paper which was recently published, Notsu et al. (2020, MNRAS, 499, 2229).
https://doi.org/10.1093/mnras/staa2944

:&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(planet1127){11/27}; Kazuaki A. Homma, Vertical growth of dust particles with UV-irradiation and organic-synthesis in protoplanetary disks|
Refractory organic matter found in the solar-system would play important roles in life and planet formation. It is important to reveal how the organic-matter was formed. One possible scenario is that they form by UV irradiation and subsequent heating of volatile ices on the dust particles in protoplanetary disks (Ciesla & Sandford (2012)). Ciesla & Sandford (2012) simulated the motion of dust particles in the protoplanetary disk and calculated the total UV-photon dosage on dust particles. They also estimated how much amount of the organic-matter would be formed from the total UV-photon dosage. They found that µm-sized dust particles can absorb UV-irradiation efficiently and would contain 10 wt% of the organic matter. However, their model assumes the UV-irradiation strength without calculating the dust distribution. It is unclear whether large dust aggregates can absorb UV-radiation or not.
We study how much organic-matter can be formed on dust particles in protoplanetary disks via UV-irradiation on dust aggregates if we consider the dust size distribution. We construct a model to simulate growth, vertical transport, and UV absorption of icy aggregates in a protoplanetary disk. We find that the large dust aggregates can contain the irradiated-dust particles, due to the fragmentation of dust aggregates and the turbulent transportation of dust particles. We also estimate the amount of organic-matter formed on the dust particles by the UV-irradiation dosage. Our results suggest that the non-sticky dust particle in strong turbulent disks can contain the same amount of organic-matter as interplanetary dust particles.

:&aname(planet1011){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.

:&aname(planet1118){11/18}; Alessandro Trani,  TSUNAMI: a fast and accurate few-body code for planetary dynamics including tidal forces|
I present TSUNAMI, a fast and accurate few-body code designed to follow the evolution of self-gravitating systems. The integrator is based on Mikkola & Tanikawa's algorithmic regularization and can easily handle close encounters, highly hierarchical systems, and extreme mass ratios. TSUNAMI includes post-Newtonian corrections and treatment for the equilibrium and dynamical tides, and it is thus suited to follow the evolution of planetary systems and systems of compact remnants. The code implements modern features such as a Python interface and support for other integrators (e.g. from the REBOUND package). I will display a suite of applications for TSUNAMI in the context of planetary dynamics, such as planetary scatterings, planets in binary systems and stellar encounters. Finally, I will present some results obtained with TSUNAMI on the dynamics of exomoons and their role in the high-eccentricity migration of hot Jupiters.

:&aname(planet0204){2/4}; Akihiko Fukui, 重力マイクロレンズ系外惑星探索の現状と展望|
重力マイクロレンズ法は、視線速度法やトランジット法では発見が難しい、主星から数AUの距離にある低質量惑星を発見可能な系外惑星手法である。この軌道領域は惑星形成時における雪線位置のやや外側に対応し、巨大ガス惑星が効率的に生成される場所と考えられるため、同法による惑星探索は惑星形成機構の理解を深める上で重要である。
これまでMOAを始めとする地上サーベイによって、100個程度の系外惑星が重力マイクロレンズ法で発見されてきた。これらの観測結果から、雪線距離の数倍程度外側の領域では主星との質量比で約10^-4(海王星質量程度)の惑星が最も豊富に存在することや(Suzuki et al. 2016)、惑星の質量比頻度分布が従来の惑星形成モデルでは説明が難しいことなどが明らかとなった(Suzuki et al. 2018)。一方、従来のサーベイでは惑星の正確な質量を決められないイベントも多く、かつ発見出来る軌道領域も雪線距離の数倍程度に限られていた。
2025年頃に打ち上げ予定のWFIRSTでは、スペースから銀河中心方向において精密重力マイクロレンズサーベイが行われ、水星質量以下の惑星を含む約2千個の系外惑星が発見される見込みである。それらの多くは正確な質量も測ることができ、またより幅広い軌道領域で発見が期待されるため、遠方惑星の詳細な軌道-質量分布が描き出されると期待される。一方、近年、銀河面においてより距離が近い星を光源とする重力マイクロレンズイベントが発見され始め、近傍重力マイクロレンズ惑星探索の可能性も見えてきた。そのような近傍イベントではレンズ星が明るいため、分光観測を含め様々な詳細観測が期待される。本講演では、上記のような重力マイクロレンズ法による系外惑星探索の現状と展望を紹介する。

:&aname(planet0227){2/27}; Masanobu Kunitomo, Coevolution of a star and planets in the pre- and post-main-sequence phases|
I will talk about two subjects in the context of the coevolution of a central star and planets. One is the pre-main-sequence evolution of low-mass stars. Recent hydrodynamic simulations have revealed that materials accrete onto protostars through disks rather than spherical accretion. Given this new framework, recent theoretical work has shown that pre-main-sequence evolution is affected by the energy deposited inside the star by accretion. We performed stellar evolutionary simulations of low-mass stars and found that deuterium burning also regulates the pre-main-sequence evolution. From the comparison with observation in the H-R diagram, we confirm that the luminosity spread seen in clusters can be explained by models with a somewhat inefficient injection of accretion heat. We also discuss the influence of planet formation on the stellar surface composition.
The other is the orbital evolution of planets beyond the main sequence. Observations have revealed the lack of close-in (<~0.6 au) planets around GK clump giants unlike solar-type main-sequence stars. We examine the possibility that close-in planets have been engulfed by the host stars during the RGB phase due to tidal decay. We integrate numerically the post-main-sequence evolution of stars and the orbital evolution of planets. We derive the survival limit inside which the planets are eventually engulfed by their host stars. We found that all the detected planets are beyond the survival limit. However, on the high-mass side (>2.1 solar mass), the detected planets ore orbiting significantly far from the survival limit, which suggests the engulfment may not be the main reason for the observed lack of close-in giant planets.

:&aname(planet0305){3/5}; Kenji Kurosaki, Giant impact on ice giants in the proto-planetary disk|
Our solar system has two ice giants, Uranus and Neptune. Those planets have similar mass and radius but different obliquity and the intrinsic luminosity. Differences between Uranus and Neptune suggest origins of those planets. Ice giants was formed by collisions among large planetary embryo in the outer region of the proto-planetary disk. Thus, the ice giants’ obliquities imply the histories of giant impacts during their formation. Previous studies for giant impact simulation for ice giants suggest that 1-3 Earth mass impactor can reproduce the present rotational angular momentums of Uranus and Neptune. Those impactors possibly have the atmosphere came from the disk gas, though the atmosphere for the impactor have not considered by previous studies. In this study, we use the Godunov-type Smoothed Particle Hydrodynamic simulation to calculate the giant impact on the planets with the hydrogen helium atmosphere. I will talk about the planetary mass, the angular momentum, and the atmospheric mass after the impact and discuss the origin of the ice giants.