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OUTAP Colloquium 2013

ホーム > コロキウム & セミナー > 宇宙進化コロキウムのご案内 > 2013年度の宇宙進化コロキウム
・・・・・2013年度の宇宙進化コロキウム・・・・・

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講演者 : 水野 陽介 氏(清華大學)/SPEAKER : Dr. Mizuno (Tsing-Hua Univ.)
TITLE : Current-Driven Kink Instability in Magnetically Dominated Relativistic Jets
DATE : 3/27 (wed) 15:00 ~
LOCATION: F608

ABSTRACT:
We have investigated the temporal development of current-driven (CD) kink instability in magnetically dominated relativistic jets via 3D relativistic MHD simulations. In this investigation, a static force-free equilibrium helical magnetic configuration is considered in order to study the influence of the initial configuration on the linear and nonlinear evolution of the instability. We found that the initial configuration is strongly distorted but not disrupted by the CD kink instability. The linear growth and nonlinear evolution of the CD kink instability depends moderately on the radial density profile and strongly on the magnetic pitch profile. We also present the influence of jet rotation on the temporal development of the CD kink instability. We briefly discuss implications of our findings for Poynting-dominated jets.

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講演者 : 郡 和範 氏(高エネルギー加速器研究機構)/SPEAKER : Prof. Kohri (KEK)
TITLE :21cm, gravitational wave, and PBH or UCMH formations to observe small-scale fluctuations
DATE : 3/5 (wed) 15:00 ~
LOCATION: F313

ABSTRACT:
In some classes of inflation models such as type-III hilltop inflation models, large curvature fluctuations are predicted at small scales with satisfying the current observational data reported by Planck, WMAP 9 year and so on. We show that we can discriminate these types of models from others by observing the small-scale fluctuations through future observations of mu-distortion, 21cm fluctuations, gravitational wave, or using bounds from Primordial Black Hole or Ultra Compact Mini Halo (UCMH) formations.



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講演者 : 西澤 篤志 氏(京都大学)/SPEAKER : Dr. Nishizawa (Kyoto Univ.)
TITLE :Test of Alternative Theory of Gravity with Gravitational-wave Polarizations
DATE : 1/8 (wed) 15:00 ~
LOCATION: F313

ABSTRACT:
In a general metric theory of gravitation, six polarizations of a gravitational wave are allowed: two scalar and two vector modes, in addition to two tensor modes in general relativity. Such additional polarization modes appear due to additional degrees of freedom in modified gravity theories. Also gravitons can be massive in modified gravity theories. We will report the method that searches for such gravitational waves with additional polarizations and graviton mass in a model-independent way.


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講演者 : 本間 希樹 氏(国立天文台水沢VLBI観測所)/SPEAKER : Prof. Honma (NAOJ Mizusawa)
TITLE : VLBI天文学の最前線:銀河系構造からブラックホールまで
DATE : 12/11 (wed) 15:00 ~
LOCATION: F313

ABSTRACT:
VLBI(超長基線電波干渉計)の技術を用いた観測天文学の最前線について紹介 する。まず国立天文台が銀河系の3次元測量を目的に現在運用しているVERA プロジェクトについて紹介し、その最新の成果についてまとめる。さらに、 VLBI技術をミリ波サブミリ波へ展開することで超巨大ブラックホールの 直接撮像を目指す「サブミリ波VLBI」の現状についても紹介し、ブラック ホール研究の今後の展望についても述べる。また、関連して、最近画像 再構成や観測データのモデリングの分野で注目されつつある、疎性モデリング/ 圧縮センシングの技術についても簡単に紹介し、VLBI分野を含む様々な 分野での応用の可能性についても述べる。

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講演者 : 尾田 欣也 氏(大阪大学)/SPEAKER : Prof. Oda (Osaka Univ.)
TITLE :Minimal Higgs inflation
DATE : 11/27 (wed) 15:00 ~
LOCATION: F313

ABSTRACT:
All the parameters in the Standard Model of particle physics have been fixed by the discovery of the Higgs particle. Observed experimental values suggest that the Higgs potential becomes flat at a very large scale. In the ordinary Higgs inflation scenario, a large non-minimal coupling between the Higgs field and the Ricci scalar is required in order to achieve a slow-roll inflation that is consistent with the observed WMAP/Planck data. Here we pursue a possibility that the Higgs potential is modified to be flat above an ultraviolet cutoff scale and that the inflation is achieved without the non-minimal coupling.


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講演者 : 鈴木 建 氏(名古屋大学)/SPEAKER : Prof. Suzuki (Nagoya Univ.)
TITLE :Roles of MHD turbulence in protoplanetary disks
DATE : 11/6 (wed) 15:00 ~
LOCATION: F313

ABSTRACT:
I introduce some results of our recent numerical simulations on accretion disks threaded with vertical magnetic field in both local and global simulation boxes with particular focus on protoplanetary disks. I present vertical outflows which are driven by the Poynting flux associated with the MHD turbulence triggered by MRI. I discuss their roles in the evolution of disks from various aspects. In addition, I plan to introduce some related topics, such as saturation of alpha values, based on our simulations.

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講演者 : 須佐 元 氏(甲南大学)/SPEAKER : Prof. Susa (Konan Univ.)
TITLE :The mass of the first stars
DATE : 10/23 (wed) 15:00 ~
LOCATION: F313

ABSTRACT:
We perform a three-dimensional radiation hydrodynamics simulation to investigate the formation of the first stars from the initial collapse of a primordial gas cloud to the formation and growth of protostars. The simulation is integrated until ~0.1 Myr after the formation of the primary protostar, by which time the protostars have already settled onto the main sequence. This work represents the first attempt at simulating the first episodes of star formation, taking into account the ultraviolet radiative feedback effect from multiple protostars as well as the three-dimensional effects of the fragmentation of the accretion disk. We find that the mass accretion onto Population III protostars is significantly suppressed by their radiative feedback. As a result, we find five stars formed in this particular simulation. The final masses of the stars are <~ 60 M ⊙, including a star of 4.4 M ⊙. Formation of such a star hints at the existence of even lower-mass stars that would live today. In addition, we also have performed simulations on 60 minihalos in order to obtain statistical characters of first stars, and the results will be discussed in the talk.

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講演者 : Vorobyov氏(ウィーン大学)/SPEAKER : Dr. Vorobyov (Univ. of Vienna)
TITLE : Fragmentation of protostellar disks and its implications for star and planet formation
DATE : 10/17 (wed) 15:00 ~
LOCATION: F608

ABSTRACT:
Gravitational instability and fragmentation of embedded protostellar disks appears to be a common occurrence, though their importance has not been fully appreciated until recently. Using numerical hydrodynamics modeling, I will demonstrate how disk fragmentation can lead to the formation of giant planets on wide orbits and freely floating brown dwarfs. Episodic accretion onto the protostar, an effect that can explain both the spread and magnitude of luminosities in young star-forming regions and FU Orionis-type luminosity outbursts, can also be triggered by disk fragmentation. Finally, I will show how disk fragmentation can influence the CO ice content in protostellar disks and envelopes and account for the presence of crystalline silicates in the Solar System comets.

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講演者 : 井上 昭雄 氏(大阪産業大学)/SPEAKER : Prof. Inoue (Osaka Sangyo Univ.)
TITLE : Lyman bump galaxies: a new population of high-z galaxies emitting strong Lyman continuum
DATE : 10/16 (wed) 15:00 ~
LOCATION: F313

ABSTRACT:
The source responsible for the cosmic reionization is still unknown, while the young star-forming galaxies in the early Universe is the leading candidate. However, the Lyman continuum emissivity of galaxies was rarely measured until recently. Our Subaru project observing Lyman continuum of z=3 galaxies has revolutionized the situation by finding many unexpectedly strong Lyman continuum emitters. Some of the galaxies are brighter at the rest-frame 900A than at 1500A, which means a Lyman "bump" not "break". Escaping nebular continuum can explain such an unusual spectral feature we found.

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講演者 : 橋本 幸士 氏(大阪大学)/SPEAKER : Prof. Hashimoto (Osaka Univ.)
TITLE : From superstring to condensed matter physics
DATE : 10/9 (wed) 14:00〜
LOCATION: F313

ABSTRACT:
Superstring theory has been served as a candidate for a theory unifying all matter and forces in the universe. Along its theoretical development, a new "principle" was found: "holographic principle", in other words, "AdS/CFT correspondence". This new principle creates bridges between various subjects in physics: gravity, particle physics, condensed matter and nuclear physics. In this talk, I explain the new principle in plain words, and tell you how it works, how it can be applied, and how it can put an access to grand challenges in physics.

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講演者 : 星野 真弘 氏(東京大学)/SPEAKER : Prof. Hoshino (Univ. of Tokyo)
TITLE : Particle Acceleration and Angular Momentum Transport by Magnetorotational Instability (MRI) in Collisionless Accretion Disks
DATE : 10/4 (Fri) 14:30〜
LOCATION: D401

ABSTRACT:
Particle acceleration and angular momentum transport during the magneto-rotational instability (MRI) in a collisionless accretion disk is investigated by using a 3d particle-in-cell simulation. The MRI is known to play an important role on the formation of accretion disk, and the nonlinear time evolution of MRI has been extensively investigated by means of MHD simulations by numerous people. However, our understanding of the kinetic (collisionless) behavior of MRI is limited. In this talk, we argue the kinetic MRI by focusing on the role of magnetic reconnection for angular momentum transport and particle acceleration. We show that the plasma pressure anisotropy induced by the action of MRI dynamo leads to the rapid growth of magnetic reconnection, and as the result the non-thermal particles with a hard power-law spectrum as well as the strong MHD turbulence are quickly generated. We also discuss that the kinetic MRI is one of plausible mechanisms to explain the nonthermal particles observed around a massive black hole of Sgr A*.

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講演者 : 羽澄 昌史 氏(KEK)/SPEAKER : Prof. M. Hazumi (KEK)
TITLE : Cosmic Microwave Background Polarization Measurements (PDF file)
DATE : 9/02 (Mon) 15:00〜
LOCATION: F608

ABSTRACT:
Cosmological inflation, which is the leading hypothesis to resolve the problems in the Big Bang theory, predicts that primordial gravitational waves were created during the inflationary era. Measurements of polarization of the cosmic microwave background (CMB) are known as the best probe to detect the primordial gravitational waves. While the discovery of gravitational waves would in itself be a landmark event, it would also have a profound impact on cosmology; this is because it would allow us to determine the energy scale of the inflation. From the viewpoint of high-energy physics, the energy scale of the grand unified theories (GUTs) is a very natural energy scale for the occurrence of inflation. Further, next-generation CMB polarization experiments are expected to be sufficiently sensitive to explore the GUT scale. Precision CMB polarization measurements will also provide significant improvements on other topics in particle cosmology, including sum of neutrino masses, new particles such as gravitons, early dark energy, gravitational parity violation and so on. Therefore, CMB polarization is a unique tool for studies in both cosmology and high-energy physics. In this talk, the current experimental status and prospects of future projects will be discussed, emphasizing two key projects, POLARBEAR and LiteBIRD, in which the Japanese group is involved.

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講演者 : 深川 美里 氏(大阪大学)/SPEAKER : Prof. M. Fukagawa (Osaka Univ.)
TITLE : ALMA observations of an asymmetrically-gapped protoplanetary disk
DATE : 7/17 (Wed) 14:00〜
LOCATION: F313

ABSTRACT:
Young stars are ubiquitously known to be surrounded by rotating disks consisting of gas and dust. They are potential sites where planets are born, thus they are called protoplanetary disks. However, there are few direct observational evidence of ongoing planet formation. The young star named HD 142527 is surrounded by a disk exhibiting a wide gap with a radial width of approximately 100 AU (0.7 arcsec), which makes it one of the ideal targets for Early Science with ALMA. In our observations at 340 GHz, the outer disk was readily resolved in dust continuum and molecular lines of 13CO(3-2) and C18O(3-2), with an angular resolution of about 0.4 arcsec. In the continuum, the northern part of the outer disk, at about 150 AU from the central star, is brighter than the southern area by more than one order of magnitude. In addition, the brightness temperature of the northern peak is significantly higher than the typical value found at 150 AU for other disks. The dust surface density at this location was estimated using the grain temperature constrained by the optically thick 13CO data. The derived surface density suggests gravitational instability if a gas-to-dust mass ratio is 100. Alternatively, a lower gas-to-dust ratio is possible, and in this case, grain accumulation is expected, which may lead to formation of rocky bodies.

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講演者:須藤 靖 氏(東京大学)
タイトル:多重トランンジット惑星系KOI-94のplanet-planet eclipse発見とTTV解析
日時: 6月21日(金) 17:00〜
場所: F608号室

アブストラクト:
我々の太陽系では,8つの惑星の公転軸は約7度以内の精度でよく揃っており, これらは太陽の自転軸とほぼ平行である。この事実は,惑星が原始惑星系円盤と呼ばれる塵とガ スで出来た円盤を経由して誕生した証拠とされている。一方,太陽系外惑星に目を向けてみると, 惑星の公転軸と中心星の自転軸が平行ではない系も多数報告されている。これらは,中心星の前 を惑星が通過して食を起こす「トランジット」惑星系に対するロシター効果と呼ばれる現象から 推定されたものだ。しかしながらそれらはいずれも,惑星が単独で存在する系だけであり,複数 惑星系に対する観測はなされていなかった。  そこで我々は,KOI-94という4つの惑星を持つ系に着目した。これはNASAのケプラー衛星によっ て見つかった惑星系候補である。我々はこの系のすばる望遠鏡によるロシター効果観測を提案し 採択されたのが,その観測の直前にケプラー衛星のアーカイブデータを詳細に調べたところ「惑 星同士の食」という興味深い現象が起きていたことを偶然発見した。これは,2つの惑星がトラ ンジット(中心星と惑星の食)の最中に,互いに重なりあった(惑星と惑星の食)ためである。 惑星食は,中心星,2つの惑星,地球の4つの天体がほぼ完全に一直線上に並んだ場合のみに起こ る,極めて稀な現象である。  この惑星食は稀有な天文現象として興味深いのみならず,惑星系の形状に対する示唆を与えて くれる。複数の惑星のトランジット時刻が単純な2体問題の重ねあわせからの予想とずれる現象 (TTV: transit time variation)の解析を加える事で、この複数惑星の質量や離心率を測光デー タだけから推定する事に成功した。今回はこの希有な惑星系KOI-94の測光および分光観測から得 られた知見をお話ししてみたい。

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講演者:小田 寛 氏
タイトル:ブラックホール降着流の明るいハード状態
日時: 4月24日(水) 14:00〜
場所: F313号室

アブストラクト:
アウトバースト中の銀河系内ブラックホール候補天体は、 典型的には暗くX線スペクトルがハードな状態(Low/Hard状態)から 明るくソフトな状態(High/Soft状態)へと遷移する(Hard-to-Soft遷移)。 この遷移は質量降着率の上昇に伴う冷却不安定性により 放射非効率降着流(RIAF)が鉛直方向に収縮し標準円盤へ遷移する事で引き起こされる。 ところが近年の観測により2種類のHard-to-Soft遷移が報告されている。 一つは比較的低い光度でLow/Hard状態からHigh/Soft状態へ遷移するもので(暗いHard-to-Soft遷移)、 RIAFから標準円盤への遷移で説明される。もう一つはLow/Hard状態から いくつかの明るい状態を経由した後High/Soft状態に遷移し さらに遷移中に相対論的ジェット噴出を示す(明るいHard-to-Soft遷移)。 この遷移中のLow/Hard状態以降の降着流の物理状態や、ジェット噴出の 物理機構は未解明である。本発表では明るいHard-to-Soft遷移中のジェット噴出直前の状態である 明るいハード状態に焦点を当て、その理論モデル、特に磁気圧優勢円盤について述べる。
 
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コロキウムの予定表はこちら/ Schedule of colloquium