Colloquium2015 のバックアップ(No.1)
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- 1 (2016-04-05 (火) 15:57:57)
理論コロキウム2015 †
理論コロキウムは原則として毎週水曜日の午後14:10から開催しています。
原則として英語で講演していただきますが、
講師・参加者が日本人だけの場合は日本語に切り替えてくださって結構です。
台内・台外また分野を問わず広く発表者（台外の方には旅費・謝金あり）を募集しています。
お問い合わせは以下のコロキウム係までお願いします（_AT_を@に変更してください）。
- 銭谷 誠司 seiji.zenitani_AT_nao.ac.jp
- 野沢 貴也 takaya.nozawa_AT_nao.ac.jp
- Ken Chen ken.chen_AT_nao.ac.jp
- 井上 剛志
理論コロキウムの前には台内の発表者によるショートコロキウムを行っています。
Schedule & History †
2010年度 2011年度 2012年度 2013年度 2014年度
Confirmed speakers †
- 住 貴宏さん（大阪大）
- 橘 省吾さん（北大）
- 高本 亮さん（東京大）
Abstract †
- 4/1 Rolf Kuiper (Univ of Tubingen, Germany) Protostellar Outflows and Radiative Feedback in Massive Star Formation
- During their formation and early evolution, massive protostars impact on their host cores via protostellar outflows and radiation pressure. We have performed radiation hydrodynamic simulations of the formation of massive stars, including the effect of protostellar outflows and radiative feedback, starting from a pre-stellar core of dusty gas. Therein, the evolution of the stellar environment is resolved down to the order of 1 AU and the stellar irradiation feedback is computed by use of a highly accurate frequency-dependent ray-tracing approach. In contrast to previous investigations, we follow the long-term evolution of the collapse until the cessation of accretion onto the protostar and its circumstellar disk, which enables us to quantitatively derive the final efficiencies of these feedback effects. To assess the net effects of protostellar outflows, we compare these results to simulations without outflows. Initially, protostellar outflows lower the accretion rate onto the disk and protostar. However, this decrease is compensated by a longer period of accretion. The bipolar cavity formed by the protostellar outflow enhances the “flashlight effect” and thus reduces radiative feedback during later evolutionary stages. We conclude that the combined effects of kinematic feedback from protostellar outflows and radiation pressure feedback by protostars are not simply additive. For the particular initial conditions chosen for this study (100 Msol cores with varying initial density slopes) we obtain final stellar masses in the range 42 – 55 Msol. When compared to equivalent cases without an outflow, those cases with a protostellar outflow had lower average accretion rates, longer accretion times, and slightly higher final masses. Furthermore, I can report on preliminary results of our ionization feedback studies and our recent studies on the effects of synchronously ongoing stellar evolution (with the aid of the STELLAR code by Harold Yorke) as well as on the shielding properties of the inner dust-free gas disk.
- 4/13 Dimitris Stamatellos (Univ of Central Laucashire) Planet migration and gap opening in self-gravitating protoplanetary discs
- Gravitational torques between the planet and its host disc result in orbital migration of the planet and affect its subsequent evolution. Studies of migration of planets formed by core accretion (i.e. late during the disc evolution) have identified two main types of planet migration (fast/slow), depending on the mass of the planet. The discovery of massive planets orbiting at large distances from the host star suggests that at least some giant planets may form early-on during the disc evolution via disc fragmentation. Such planets will interact with a relatively massive (self- gravitating) disc. I will discuss how Jovian planets interact with self-gravitating discs, what are the effects of such interactions (inward migration, gap opening, and planetary mass growth), and how these depend on the disc thermodynamics. I will present global hydrodynamic simulations of planet-disc interaction and planet migration, and discuss whether signatures of such processes could be observed.
- 4/15 白崎正人 (理論部) 遠方銀河撮像観測とガンマ線観測の相関解析で探る暗黒物質対消滅
- 様々な大規模天文観測が示唆する標準的な宇宙模型では、現在の宇宙のエネルギー組成のうち約27%が暗黒物質と呼ばれる未知の重力源でまかなわれていると言われている。暗黒物質の存在は様々な天文観測により確実視されているものの、その物理的な性質については未だ謎に包まれている。
本発表では、暗黒物質の素粒子的な性質の一つである「対消滅現象」の痕跡を探る統計手法として、遠方銀河撮像観測とガンマ線観測の相関解析を紹介する。遠方銀河撮像観測では、宇宙に広がる物質分布により遠方銀河像がわずかに歪められる弱重力レンズ効果を観測する。一方で、ガンマ線観測では、銀河系外のガンマ線源が作るガンマ線背景放射を観測する。弱重力レンズ効果は、視線方向の暗黒物質分布により引き起こされ、その暗黒物質分布は、もし対消滅していれば、系外ガンマ線源にもなりうる。すなわち、暗黒物質対消滅が存在すれば、弱重力レンズ効果とガンマ線背景放射の空間分布には相関関係があることが期待される。
我々は、世界で初めて実際の観測データを用いて、弱重力レンズ効果とガンマ線背景放射の空間相関を測定した。測定結果とそこから導かれる暗黒物質対消滅への制限、さらに将来観測への展望について発表する。
- 4/22 道越秀吾 (理論部) 土星の環の自己重力ウェイク構造
- 土星の環には自己重力ウェイク構造とよばれる微細な渦状腕構造が存在していると考えられている。自己重力ウェイクの形成には、無衝突粒子系で議論されてきた密度増幅メカニズム(スイング増幅)が関係していると考えられてきたが、詳しい研究は行われていなかった。本研究はピッチ角に着目し、スイング増幅と自己重力ウェイクの関係を確認することが目的である。そこで研究の第一歩として、スイング増幅を理解するために、まず無衝突系において渦状腕形成の多体シミュレーションとスイング増幅の摂動解析を行い、渦状腕のピッチ角を調べた。その結果、摂動解析と多体シミュレーションがよく一致することが分かった。これは、無衝突系の渦状腕形成にはスイング増幅が関係していることを示唆している。そして、次の段階として、土星の環において同様の多体シミュレーションを行い、ピッチ角を調べた。その結果、スイング増幅の摂動解析から予想されない依存性が確認された。これはスイング増幅を土星の環に適用する場合は、より現実的なモデルへ拡張する必要があることを意味している。本発表ではこれらの研究の概要を紹介する。また時間があれば、より現実的な理論モデル構築に向けた研究のアイデアを紹介する。
- 5/20 福島登志夫 (情報センター) Precise and fast computation of generalized Fermi-Dirac integral by parameter polynomial approximation
- The generalized Fermi-Dirac integral, $F_k(\eta,\beta)$, is approximated by a group of polynomials of $\beta$ as $F_k(\eta,\beta) \approx \sum_{j=0}^J g_j \beta^j F_{k+j} (\eta)$ where $J=1(1)10$. Here $F_k(\eta)$ is the Fermi-Dirac integral of order $k$ while $g_j$ are the numerical coefficients of the single and double precision minimax polynomial approximations of the generalization factor as $\sqrt{1+x/2} \approx \sum_{j=0}^J g_j x^j$. If $\beta$ is not so large, an appropriate combination of these approximations computes $F_k(\eta,\beta)$ precisely when $\eta$ is too small to apply the optimally truncated Sommerfeld expansion (Fukushima, 2014, Appl. Math. Comp., 234, 417). For example, a degree 8 single precision polynomial approximation guarantees the 24 bit accuracy of $F_k(\eta,\beta)$ of the orders, $k=-1/2(1)5/2$, when $-\infty < \eta \le 8.92$ and $\beta \le 0.2113$. Also, a degree 7 double precision polynomial approximation assures the 15 digit accuracy of $F_k(\eta,\beta)$ of the same orders when $-\infty < \eta \le 29.33$ and $0 \le \beta \le 3.999 \times 10^{-3}$. Thanks to the piecewise minimax rational approximations of $F_k(\eta)$ (Fukushima, 2015, Appl. Math. Comp., 259, 708), the averaged CPU time of the new method is only 0.9--1.4 times that of the evaluation of the integrand of $F_k(\eta,\beta)$. Since most of $F_k(\eta)$ are commonly used in the approximation of $F_k(\eta,\beta)$ of multiple contiguous orders, the simultaneous computation of $F_k(\eta,\beta)$ of these orders is further accelerated by the factor 2--4. As a result, the new method runs 70-450 times faster than the direct numerical integration in practical applications requiring $F_k(\eta, \beta)$.
- 5/27 塚本 裕介 (理化学研究所) 星周円盤形成と進化：ホール効果によって引き起こされる円盤サイズの２峰性と自己重力円盤の構造について
- 本講演では２つの話題について発表する。 前半では円盤形成におけるホール効果の影響について報告する。分子雲コア内のガスは弱電離プラズマであるため理想MHD近似は成り立たず、非理想効果（オーム散逸、ホール効果、両極性散逸）が重要な役割を果たす。このなかで、ホール効果はpoloidal磁場からtroidal磁場を作り出し、poloidal磁場に対して左ネジの方向にガスの回転を誘起するという興味深い性質がある。しかしながら、ホール効果の円盤形成に対する影響についてはいままでほとんど調べられてこなかった。 講演者は3つの非理想効果と輻射輸送を考慮した3Dシミュレーションを行い、特にホール効果の円盤形成に与える影響について研究を行った。その結果、分子雲コアの回転ベクトルと磁場ベクトルが平行の場合、１AU程度の円盤しか形成しなかったのに対して、反平行の場合は２０AU程度の重力的に不安定な円盤が形成することがわかった。この結果は回転ベクトルと磁場ベクトルが平行か反平行かといういままで重要視されてこなかった条件が円盤形成過程を大きく変えるという点において極めて興味深い。また、中心で回転が促進されることによって角運動量保存からエンベロープが逆回転する現象が見出された。このような逆回転するエンベロープは十分観測可能であり、もし観測された場合、ホール効果が円盤の形成進化において重要な役割を果たすことの証拠となると考えられる。 後半では、自己重力的な円盤の構造についての輻射流体力学シミュレーションについて報告する。定常降着円盤モデルを考察することで、自己重力円盤の構造は回転プロファイルと温度プロファイルからきまることがわかる。したがって円盤内の輻射輸送を解き、温度構造がどのようなメカニズムで決まるかを明らかにする必要がある。そこで、講演者は輻射流体力学シミュレーションによって自己重力円盤の構造について調べた。その結果、温度が低い(100K以下)領域では動径方向に拡散的に流れる輻射輸送によって温度構造がきまり、円盤の面密度、α値はその温度構造のもとでの定常降着円盤モデルでよく記述できることがわかった。このような円盤モデルは先行研究では考察されておらず興味深い結果であると考えている。 以上の話題の他に、時間が許せば自己重力不安定による円盤分裂やその惑星形成論への応用についても議論したい。
- 6/10 Hsi-An Pan (北大) What is a Giant Molecular Cloud? Are Observers and Simulators Discussing the Same Star-forming Clouds?
- Observations and simulations have now reached the point where the giant molecular cloud (GMCs) populations can be studied over a whole galaxy. This is immensely helpful for understanding star formation, since the cloud properties set the conditions for new star birth. Yet, are these two groups really comparing the same objects? While simulators work in position-position-position (PPP) space, observers see projected properties along the line of sight, identifying clouds in position-position-velocity (PPV) space. If these methods do not identify the same objects, then the interpretation and comparisons between the data sets may be highly misleading. In this research we generated PPV and PPP data for a high-resolution simulated galaxy and compared the identified cloud properties in both data sets. Results show that the physical properties of molecular clouds in the individual galactic environments (bar, spiral, and outer disk) are highly similar among the two data structures. About 70% of clouds have single counterpart in each dataset, and their cloud properties scatter mostly within a factor of two. Therefore, comparing the simulated and the observed GMCs is practical, and it will be the trend in the ALMA era.
- 6/10 Alexander Pettitt (北大) Armed and/or dangerous: the sensitivity of galactic spiral generation in tidal encounters
- The nature of the spiral structure of disc galaxies is still somewhat of an open question. A number of different mechanism have been suggested to underpin spiral features; density waves, swing amplified transient spirals, bar driven arms and tidal encounters. The regimes where each of these mechanisms becomes dominant is an unknown, when does an interaction between a galaxy and a companion become strong enough to drown out the structure formed in isolation? We present the results of an investigation into the various morphologies created in the interaction between a disc galaxy and minor companion using numerous numerical simulations with stars, dark matter and gas. The primary goal of which is to discern the sensitivity of disc galaxies to tidal spiral structure. For what orbital paths, mass and velocity limits does the galaxy cease to feel the companion, and therefore any spiral generation is left to the galaxy itself? This also includes comparisons to transient spiral arm structures, those generated in simulations of isolated discs, and how the longevity, morphology and gas structure differs between the two mechanisms. By understanding the mechanisms driving different spiral morphologies we can better assess the origin of structure in external galaxies and the Milky Way.
- 6/17 Lukasz Stawarz (ISAS / Jagiellonian University, Poland) Particle Acceleration in Astrophysical Sources of High Energy Radiation
- Strong shocks induced in the interstellar medium by supernova explosions are widely considered as the dominant production sites of cosmic ray particle detected on Earth with enormous energies reaching 10^15 eV. Relativistic, or instead weak by extremely extended shock waves encountered in various types of extragalactic object - predominantly active galaxies and clusters of galaxies - are on the other hand typically considered as the most likely sources of even higher energy cosmic rays, up to the ultra-high energy range of 10^21 eV. In this talk I will critically re-examine the current status of our understanding of particle acceleration in astrophysical environment in general, pointing out the most recent observational findings which challenge the shock paradigm for the cosmic ray production, and emphasizing important but often ignored differences between particle acceleration processes in non-relativistic and relativistic plasma.
- 6/17 紀 基樹 (KASI) On the origin of black hole outflows
- Understanding formation mechanism of relativistic jets in active galactic nuclei (AGN) is one of the biggest issues in astrophysics. To solve the problem, outstanding question is basic energetics in the vicinity of the central black holes which ultimately power the relativistic jets. The AGN jet Messier 87 (hereafter M87) is one of the closest (16Mpc from the Earth) example of relativistic jets and it is well known as the best source to explore a jet base close to ~10 Schwarzschild radii scale with VLBI (Very Long Baseline Interferometry) radio telescopes. Here I show highlights of VLBI observations of innermost part of the M87 jet. Then, I show the results of our estimate of magnetization degree at the base of M87 down to ISCO (innermost stable circular orbit) scale based on these observational data.
- 7/8 田中 秀和（北大）惑星の種、微惑星の付着成長による形成
- 惑星形成の標準的理論では、原始惑星系円盤内でまず微惑星と呼ばれる「惑星の種」が形成され、微惑星がさらに衝突合体を繰り返すことで、最終的に惑星が作られたと考えられている。微惑星の形成メカニズムとしては、原始惑星系円盤の中心面につくられるダスト層において自己重力が作用して微惑星は形成されるという説が従来から多くの研究者により信じられてきた。しかしながら、キロメータサイズの微惑星に至る過程では自己重力は微弱であり、それが「重力説」の悩みの種となっている。我々のグループでは、ダスト衝突のＮ体数値シミュレーションを行うことにより、サブミクロン粒子の集合体であるダストの高い付着性や高空隙内部構造の形成を明らかにしてきた。さらに、ダストのこれらの性質が微惑星形成の様々な問題を解決し得ることから、微惑星は付着成長でつくられたという説を提唱している。本講演では、我々のダスト衝突のＮ体数値シミュレーション結果を紹介することで、ダスト衝突付着のメカニズムを実感し理解していただくことを目標とする。
- 7/15 簑島 敬（JAMSTEC）ブラソフシミュレーションのためのマルチモーメント移流法
- 無衝突プラズマや重力多体系の支配方程式は、無衝突ボルツマン方程式（ブラソフ方程式）である。これらの第一原理計算手法として、個々の粒子の運動方程式をラグランジュ的に追跡する粒子シミュレーションが広く用いられている。粒子シミュレーションは、アルゴリズムがシンプルでロバスト、限られた計算機資源でも実行できるといった、数値計算において極めて好ましい性質を持つ強力な手法である。一方で、粒子シミュレーション固有の弱点を解消すべく、ブラソフ方程式を6次元位相空間上で直接離散化してオイラー的に解くブラソフシミュレーションも提案され、特に静電プラズマや自己重力系などのブラソフ-ポアソン系において成功を収めている。しかしながら、本研究の対象としている宇宙プラズマは大抵磁場を帯びている。磁化プラズマのブラソフ-マクスウェルシミュレーション研究は、技術的困難などの理由から、未だ発展途上の分野である。本発表では、ブラソフシミュレーション技術と、特にブラソフ-マクスウェルシミュレーションにおける難点について紹介し、それを解消すべく我々が開発を続けている数値計算手法（マルチモーメント移流法）と、本手法を用いた磁化プラズマのブラソフシミュレーションについて紹介する。
- 7/22 長谷川 靖紘（理論部）Planet Formation: from disks to the Solar System
- Planet formation is one of the most ubiquitous processes in the Universe. As suggested by the ALMA images of HL Tau, it is currently recognized well that planet formation should be examined in the context of star formation. In addition, it is of fundamental importance to apply our understanding of planet formation to origins of the Solar system. In this talk, I will present some of the results of my recent projects that have been and are being developed with scientists at NAOJ. These include the observational and theoretical investigation of HL Tau, the stability analysis of protoplanetary disks by magnetorotational instabilities (MRIs), and formation of chondrules via planetesimal collisions. While many of these results are still preliminary, I will attempt to give some flavor of what I have done at NAOJ since last Sept.
- 10/1 Yutaka Komiya（Univ. of Tokyo）Chemical evolution of r-process elements
- The main astronomical source of the r-process element has not yet been identified. Two sites have been suggested, core-collapse supernovae and neutron star mergers (NSMs). From perspective of the Galactic chemical evolution, it has been pointed out that the NSM scenario is incompatible with observations, while nucleosynthetic studies favor the NSM scenario. Recently, however, Tsujimoto & Shigeyama (2014) pointed out that the NSM ejecta can spread into much larger volume than the ejecta from a supernova. We re-examine the chemical evolution of r-process elements under the NSM scenario considering this difference in propagation of the ejecta. We show results of our new chemical evolution model for the Milky Way and dwarf galaxies. We find that the NSM scenario can be compatible with the observed abundances of the Milky Way halo stars. We also discuss the difference of abundance patterns between galaxies.
- 10/7 Aleksander Sadowski（MIT）How not to lose photons when simulating radiative black hole accretion in general relativity
- In this talk I will summarize the recent progress in simulating optically thick black hole accretion. In detail, I will describe simulations of super-critical black hole accretion disks applicable to ultra luminous X-ray sources and tidal disruption events. Special attention will be paid to their luminosities and mildly relativistic, radiative jets formed in such systems. I will introduce a photon-conserving method of treating Comptonization and show how it can be coupled with sophisticated radiation transfer solvers to obtain stets-of-art synthetic spectra of accretion disks.
- 10/14 Ken Wong (DTA）Strong Gravitational Lensing as a Probe of Galaxy Evolution and Cosmology
- Strong gravitational lensing is a useful probe for studying the evolution of galaxies over cosmic time, as well as the cosmological parameters of the universe. I will review a series of lensing projects that I am involved in, including 1) using galaxy cluster-scale lenses to magnify high-redshift galaxies, 2) studying the innermost mass distribution of a galaxy-scale lens and constraining the mass of its supermassive black hole, 3) using lensed quasars with measured time delays to constrain the Hubble constant, among other cosmological parameters, and 4) accounting for line-of-sight effects in time delay lenses, which can bias lens modeling results if not properly accounted for. These diverse projects demonstrate the application of using strong lensing at various scales as a tool to answer fundamental questions about extragalactic astronomy and cosmology.
- 10/14 Ken Chen (DTA）The Cosmic Dawn : Physics of the First Luminous Objects
- One of the paramount problems in modern cosmology is to elucidate how the first generation of luminous objects, stars, accreting black holes (BHs) and galaxies, shaped the early universe at the end of the cosmic dark ages. According to the modern theory of cosmological structure formation, the hierarchical assembly of dark matter (DM) halos provided the gravitational potential wells that allowed gas to form stars and galaxies inside them. Modern large telescopes have pushed the detection of galaxies up to a redshift of z ~ 10. However, models of the first luminous objects still require considerable effort to reach the level of sophistication necessary for meaningful predictions. Due to the complexity of involved physical phenomena, this physical understanding may only come by the proper use of numerical simulations. Therefore, I have used state-of-the-art simulations on some of largest supercomputers to study these objects. In my talk, I will discuss the possible physics behind the formation of these first luminous objects by presenting the results from our simulations. I will also give possible observational signatures of the cosmic dawn that will be the prime targets for the future telescopes such as the James Webb Space Telescope (JWST).
- 10/21 Hirotomo Noda (RISE project, NAOJ) Planetary laser altimeters
- I will review science outputs and hardware basics of the laser altimeters for lunar and planetary sciences which I have involved in. The laser altimeters aboard Kaguya, Hayabusa2 and JUICE will be mentioned.
- 11/4 Yasunori Hori (ABC, NAOJ) How Does a Collision Sculpture a Super-Earth in the Proximity of Stars?
- The Kepler mission has revealed the prevalence of volatile-rich/poor low-mass planets in the proximity of host stars. Several post-formation processes have hitherto been proposed for explaining the origin of volatile inventory of those planets: a mass loss via a stellar XUV irradiation and Parker wind, degassing of accreted material, and in-situ accumulation of the disk gas. However, the compositional dissimilarity between neighboring planets on adjacent orbits such as Kepler-36 and Kepler-11 systems is puzzling for the three processes. We consider the possibility of a collisional origin for the coexistence of volatile-poor super-Earths and mini-Neptunes in a tightly-packed system. We performed three-dimensional hydrodynamic simulations of giant impacts on a super-Earth with a H/He atmosphere. A high-speed collision can strip off most of the original H/He atmosphere, as we expected. A hot and inflated planet after the giant impact cools down so slowly that a prolonged lifetime of the extended post-impact atmosphere enhances mass loss via a Parker wind and subsequent hydrodynamic escape driven by a stellar XUV irradiation. We also found that a low-speed head-on collision results in the appearance of a positive-compositional gradient deep inside the planet which leads to an inefficient heat transport via double-diffusive convection, whereas a high-speed one can homogenize a distribution of heavy elements above the core.
- 11/18 Kazem Ardaneh (U of Tsukuba) Collisionless Weibel shocks and electron acceleration in gamma-ray bursts
- A study of collisionless external shocks in gamma-ray bursts is presented. The shock structure, electromagnetic fields, and process of electron acceleration are assessed by performing a self-consistent 3D particle-in-cell (PIC) simulation. In accordance with hydrodynamic shock systems, the shock consists of a reverse shock (RS) and forward shock (FS) separated by a contact discontinuity (CD). The development and structure are controlled by the ion Weibel instability. The ion filaments are sources of strong transverse electromagnetic fields at both sides of the double shock structure over a length of 30 - 100 ion skin depths. Electrons are heated up to a maximum energy E_ele = E_b**0.5, where E_ele is the energy normalized tothe total incoming energy. Jet electrons are trapped in the RS transition region due to the presence of an ambipolar electric field and reflection by the strong transverse magnetic fields in the shocked region. In a process similar to shock surfing acceleration (SSA) for ions, electrons experience drift motion and acceleration by ion filament transverse electric fields in the plane perpendicular to the shock propagation direction. Ultimately accelerated jet electrons are convected back into the upstream. The FS region shows the characteristic of a double layer plasma. In this region, acceleration of the electrons by the double layer electric fields creates a power-law distributed population in the electron distribution function. In the present work, the power-law index for the electron distribution function in the precursor region is α =1.8, which can be associated to the radio afterglow emission.
- 11/25 Wing-Kit Lee (Academia Sinica) Spiral Structure in Disks
- I will review some mechanisms for generating spiral structures in astrophysical disk systems such as galaxies and protoplanetary disks. In particular, I will talk about my research on instabilities of the galactic spiral arms, namely feathering instability. In addition, I will introduce some of my attempts to understand the three-dimensional spiral shocks in a protoplanetary disk.
- 12/2 Tjarda, Boekholt (Leiden U) Chaos in N-body systems: Application to triple stars and Halley's comet
- N-body simulations are used to study the dynamical evolution of planetary systems, star clusters, galaxies and large scale structure. These systems are often chaotic, in the sense that they are highly sensitive to initial conditions. In the first part of my talk, I focus on the growth of small numerical errors, to determine the reliability of N-body results, specifically those of chaotic triple systems. In the second part I study the growth of a small, physical perturbation in order to study the stability of the orbit of comet Halley.
- 12/09 Shingo Hirano (Univ. of Tokyo) Wide Mass Distribution of Primordial Stars: Various Star Formation in the Early Universe
- Primordial stars, so-called Population III stars, play vital roles in the early cosmic evolution. The stellar evolution and death, which regulate the dynamical, radiative, and chemical feedbacks to the surrounding medium, are largely determined by its stellar mass. The characteristic mass, or initial mass function, of Pop III stars is thus essential to understand the formation and evolution of the first galaxy. This talk introduces theoretical study on various formation paths of the first-generation stars and the distribution of their final masses. A series of numerical simulations from the formation of star-forming cloud to the end of the mass accretion onto the protostar are performed to determine the initial stellar mass. The simulation results show a certain dependence of the stellar masses on the initial state of star-forming clouds. By using such a correlation, a large sample of primordial star-forming clouds in the cosmological volume is converted to the mass distribution of the primordial stars. This is the first study to directly calculate the stellar mass distribution in the early universe theoretically. I will also introduce our recent study about formation of supermassive first star with 100,000 solar-masses which can become a seed of high-z quasar.
- 12/16 Lucie Jilkova (Leiden Observatory) Mass transfer between debris discs during close stellar encounters
- Stars are born in clustered environment and planetary systems are born around stars. Stars in clusters gravitationally interact and experience close encounters that have a direct influence on their planetary systems. I will present results on simulations of mass transfer among debris (planetesimal) discs during close stellar encounters that happen in star clusters. We explored the parameter space of the encounters and mapped the orbits of the transferred planetesimals around their parent star as well as around their new host. Depending on encounter parameters, a substantial part of the disc can be captured by the other star and the captured objects have specific orbits. We expect that many stars experienced transfer among their debris discs and planetary systems in their birth environment and I will present the implications of this process for the Solar system.
- 12/17 Thiem Hoang (CITA) Polarization of Anomalous Microwave Emission from Spinning Dust and Magnetic Dust
- Anomalous microwave emission (AME) in the 10-60 GHz frequency range is an important Galactic foreground component that contaminates the cosmic microwave background (CMB) radiation, which was discovered 20 years ago in the course of data analysis from COBE. With the explosion of CMB experiments hunting for primordial gravitational waves from the early universe through the CMB B-mode signal, a pressing issue is to have an accurate model of the AME polarization for reliable removal of CMB foregrounds and correct measurements of the B-mode signal. In this talk, I will first review two mechanisms suggested as origins of AME, including electric dipole emission from rapidly spinning tiny dust grains and magnetic dipole emission from ferromagnetic/ferrimagnetic nanoparticles. Then, I will discuss theoretical foundations for the polarization of AME and present our new results on quantifying the polarization of spinning dust emission and magnetic dust emission. I will compare the theoretical predictions with available observational data and discuss its implications for understanding the origin of AME.
- 1/13 Alexandre Lazarian (U. Wisconsin - Madison) Star Formation Mediated by Reconnection Diffusion
- Turbulent reconnection entails violation of flux freezing in turbulent fluids. The whole paradigm of star formation was based on flux freezing and ambipolar diffusion as a way to circumvent the flux freezing constraint. Therefore this paradigm should be changed as reconnection induces a process that I term "reconnection diffusion". I shall provide evidence for turbulent reconnection being fast and violating flux conservation and will show the numerical studies of reconnection diffusion for diffuse media, molecular clouds and accretion disks. A comparison with observations will be provided.
- 1/20 Ronin Wu (Univ. of Tokyo) Spatially resolved physical conditions of molecular gas: a zoom-in from circumnuclear region of M83 to Carina nebula
- Since the launch of the Herschel Space Observatory (Pilbratt et al. 2010), our understanding about the photodissociation regions (PDR) has taken a step forward. In the bandwidth of the Fourier Transform Spectrometer (FTS) of the Spectral and Photometric Imaging REceiver (SPIRE) on board Herschel, ten CO rotational transitions, including J = 4-3 to J = 13-12, and three fine structure lines, including [CI] 609, [CI] 370, and [NII] 250 m, are covered. This presentation focuses on the physical conditions of molecular gas probed by the Herschel SPIRE/FTS.
Based on the spatially resolved physical parameters derived from the CO spectral line energy distribution (SLED) map and the comparisons with the dust properties and starformation tracers, I will first present our findings at the circumnuclear region of M83 (Wu et al. 2015), and then zoom in toward the molecular cloud near a young open cluster, Trumpler 14, in Carina nebula. I will discuss (1) the potential of using [NII] 250 and [CI] 370 micron as star formation tracers; (2) the reliability of tracing molecular gas with CO (3) the excitation mechanisms of warm CO (4) the possibility of studying stellar feedback by tracing the thermal pressure of intersetllar molecular gas.
- 2/3 磯江 麻里 (DTA/Univ. of Tokyo) Exoplanetary System Architecture: Planetary Multiplicity and Mass Effects
- 2015年11月までに視線速度観測法とトランジット法で観測された1811個の惑星を用い、惑星系の軌道構造の惑星数や惑星系質量への依存性を統計的に明らかにすることで、惑星系形成・進化モデルへの新たな制限の可能性を探る。惑星系は、系の惑星数、中心星の質量で規格化した最大惑星質量、中心星の進化段階の3個のパラメータで分類し、それぞれの惑星系の構造を統計的に調べた。本研究では特に軌道離心率、隣接軌道間隔、惑星の質量分布に注目した。
その結果、KS検定により、大質量惑星系と小質量惑星系の軌道離心率の分布は異なることがわかった。特に0.6より大きい軌道離心率は1惑星系または2惑星系かつ、大質量惑星系にのみ存在する。また、系の角運動量欠損は惑星数の増加に伴い減少することがわかった。これは系内の惑星が多くなるほど、系が安定であるためにはそれぞれの惑星の軌道が円軌道に近くなければならないことを意味する。更に、主系列星周りの小質量惑星系では、惑星のヒル半径で規格化した軌道間隔が15-30の範囲で、惑星数に対しておよそ-1/2乗の反相関性があることが確認された。また、軌道間隔には中心星の進化段階の依存性が見られ、主系列星周りの惑星系に比べ、巨星周りの惑星系で軌道間隔が狭くなる傾向がある。惑星系の質量分布を見ると、大質量惑星系に比べ、小質量惑星系はその惑星の質量が等分配される傾向がある。発表では複数惑星系の軌道構造の統計的性質についてまとめ、その形成論的な意味について議論する。
- 2/10 Toshio FUKUSHIMA (NAOJ) Rotation curve of M33 explained by dark matter disc
- We developed a numerical method to compute the gravitational field of an infinitely-thin axisymmetric disc with an arbitrary profile of the surface mass density. We evaluate the gravitational potential by a split quadrature using the double exponential rule and obtain the acceleration vector by numerically differentiating the potential by Ridder's algorithm. The new method is of around 12 digit accuracy and sufficiently fast because requiring only one-dimensional integration. By using the new method, we show the rotation curve of some non-trivial discs: (i) truncated power-law discs, (ii) discs with a non-negligible center hole, (iii) truncated Mestel discs with edge-softening, (iv) double power-law discs, (v) exponentially-damped power-law discs, and (vi) an exponential disc with a sinusoidal modulation of the density profile. Also, we present a couple of model fittings to the observed rotation curve of M33: (i) the standard deconvolution by assuming a spherical distribution of the dark matter and (ii) a direct fit of infinitely-thin disc mass with a double power-law distribution of the surface mass density. Although the number of free parameters is a little larger, the latter model provides a significantly better fit. The determined profile of the surface mass density of the disc is significantly larger than those of the observed stars and gas. This hints a disc-like distribution of the dark matter.
- 2/17 Nobumitsu Yokoi (Institute of Industrial Science, University of Tokyo) Global flow induction by helicity: A closure approach to inhomogeneous turbulence
- With accompanied by large-scale inhomogeneous fields, such as rotation, velocity strain, magnetic field, density stratification, radiation, astrophysical turbulence is not homogeneous isotropic, but highly inhomogeneous and anisotropic. Also due to these fields, some symmetry in turbulence is often broken. These conditions of astrophysical turbulence suggest that, in treating astrophysical turbulence, we have to incorporate the following two features: (i) nonlinear interactions between large-scale inhomogeneities and small-scale turbulence; (ii) dynamic balance between transport enhancement and suppression. In this talk, after a brief introduction to turbulence, a few closure approaches to inhomogeneous turbulence are outlined. Special references are made to turbulence modeling based on a renormalized perturbation theory with multiple-scale analysis. Among several interesting applications in the astrophysical context, turbulent vortex dynamo - global flow generation and sustainment mechanism through turbulence - is discussed as an illustrative example. In non-mirrorsymmetric turbulence, turbulent kinetic helicity (velocity--vorticity correlation) as well as turbulent energy represents the statistical properties of turbulence. In such a system, an enhanced momentum transport due to eddy viscosity coupled with the mean velocity strain can be counterbalanced by the helicity effect coupled with the mean absolute vorticity. This helicity effect may induce a global vortical flow structure without resorting to any baroclinicity (obliqueness between the density and pressure gradients) effect. Validation of the theoretical predictions through direct numerical simulations (DNSs) is also presented.
References: (1) http://arxiv.org/abs/1511.08983 (2) http://www.tandfonline.com/doi/abs/10.1080/03091929.2012.754022
- 3/2 Yichen Zhang(Chile/Yale) Star Formation across the Mass Spectrum and Environments
- One of the major question in star formation is whether high and low-mass stars form in a similar way by accreting from pre-existing cores (core accretion). My talk will be around three aspects of this question. First, in the core accretion scenario, the outflow feedback is believed to be responsible for dispersing the core and regulating the core-to-star efficiency. I will present results of our recent ALMA observation of the low-mass HH 46/47 molecular outflow to understand the outflow feedback. Using 13CO and C18O emission to correct for the 12CO optical depth and trace denser and slower outflow material than 12CO only, we accurately estimated the mass, momentum and kinetic energy of the outflow. The estimated outflow properties indicate that the outflow is capable to disperse the parent core within the typical lifetime of the embedded phase of a low-mass protostar, and is regulating the core-to-star efficiency to about 1/4 to 1/3. This new observation also reveals a rotating/infalling envelope, a spinning outflow, and detailed outflow structures which help us to understand the outflow entrainment process. Second, through radiation transfer (RT) simulation, predictions of core accretion model and continuum observations of massive protostars are compared. I will introduce our evolutionary model of (massive) star formation based on the core accretion, which self-consistently includes protostellar evolution, collapse of the core, growth of the disk, and gradual opening-up of the outflow cavity. In such a framework, the evolutionary tracks are determined by the initial environmental conditions: the initial core mass, the mass surface density of the ambient clump, and the rotation of the core. Through RT simulations, we are able to produce temperature structures, SED, IR continuum images of protostars at different evolutionary stages under various initial conditions. I will show an example that such a model can interpret the multiwavelength observations of massive protostars. Third, the core accretion theory also predicts that the thermal/chemical evolution of protostellar cores can be strongly affected by the star-forming environment, e.g. a low-mass-surface-density region where low-mass stars form in relative isolation, like Taurus, vs. a crowded high-mass-surface-density region, like Orion. I will discuss this effect by combining the above RT model with simple chemical models.