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Colloquium のバックアップ差分(No.13)


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#norelated
* 理論コロキウム2016 [#z407468f]

理論コロキウムは原則として毎週水曜日の午後13:30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)。~

- 滝脇知也 takiwaki.tomoya_AT_nao.ac.jp~
- 守屋 尭 takashi.moriya_AT_nao.ac.jp~
- Kenneth Wong ken.wong ATM nao.ac.jp~
- 高橋 博之 takahashi ATM cfca.jp~
- 平居 悠 yutaka.hirai ATM nao.ac.jp

//~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>Short]]を行っています。 

** Schedule & History [#j2453518]

[[2010年度:http://th.nao.ac.jp/seminar/colloquium/2010/]]
[[2011年度:http://th.nao.ac.jp/seminar/colloquium/2011/index_2011.html]]
[[2012年度:http://th.nao.ac.jp/seminar/colloquium/2012/]] 
[[2013年度:http://th.nao.ac.jp/seminar/colloquium/2013/]] 
[[2014年度:http://th.nao.ac.jp/seminar/?Colloquium2014]] 
[[2015年度:http://th.nao.ac.jp/seminar/?Colloquium2015]] 


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|Date|Speaker|Title|Place/Time|remarks|h
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|[[4/6>#long0406]]|all internal members|self-introduction|Conference room, Cosmos Lodge / 13:30||
|[[4/13>#long0413]]|Tomoya Takiwaki (NAOJ DTA)|A Clockwork Supernova: precision numerical experiments and their applications|Conference room, Cosmos Lodge / 13:30||
|[[4/20>#long0420]]|Yuki Tanaka (NAOJ CfCA)|Magnetically Driven Wind from Hot Gaseous Planets|Conference room, Cosmos Lodge / 13:30||
|[[4/25>#long0425]]|Kohei Inayoshi (Columbia University)|Hyper-Eddington accretion flows onto massive black holes|Lecture Room/ 13:30||
|[[4/27>#long0427]]|Tetsuo Taki (NAOJ CfCA)|Toward formation of rocky planetesimals: dust and gas density evolution at a local structure of protoplanetary disks|Conference room, Cosmos Lodge / 13:30||
|[[5/11>#long0511]]|Masahiro Ogihara (NAOJ DTA)|Formation of close-in super-Earths|Conference room, Cosmos Lodge / 13:30||
|[[5/18>#long0518]]|Takashi Moriya (NAOJ DTA)|Superluminous supernovae and their origins|Large seminar room / 13:30||
|[[5/25>#long0525]]|Yukari Ohtani (NAOJ CfCA)|TBA|Conference room, Cosmos Lodge / 13:30||
|[[6/1>#long0601]]|Shogo Tachibana (Hokkaido University)|TBA|Conference room, Cosmos Lodge / 13:30||
|[[6/8>#long0608]]|Alessandro Sonnenfeld (IPMU)|TBA|Conference room, Cosmos Lodge / 13:30||
|[[6/15>#long0615]]|Makoto Takamoto (University of Tokyo)|TBA|Conference room, Cosmos Lodge / 13:30||
|[[6/15>#long0615]]|Makoto Takamoto (University of Tokyo)|Relativistic Magnetohydrodynamic turbulence in Poynting-Dominated Plasmas and its effects on Current Sheet Dynamics|Conference room, Cosmos Lodge / 13:30||
|[[6/22>#long0622]]|Takahiro Sumi (Osaka University)|TBA|Conference room, Cosmos Lodge / 13:30||
|[[7/6>#long0706]]|Shota Kisaka (Aoyama Gakuin University)|TBA|Conference room, Cosmos Lodge / 13:30||
|[[7/13>#long0713]]|Tomoaki Matsumoto (Hosei University)|TBA|Conference room, Cosmos Lodge / 13:30||
|[[7/20>#long0720]]|Hideyuki Hotta (Chiba University)|TBA|Conference room, Cosmos Lodge / 13:30||
|[[9/21>#long0921]]|Kazunori Akiyama (MIT)|TBA|Conference room, Cosmos Lodge / 13:30||

** Confirmed speakers [#hfb505be]
Naoki Yamamoto(Keio University)

** Abstract [#id139640]

:&aname(long0413){4/13}; Tomoya Takiwaki (NAOJ DTA)  A Clockwork Supernova: precision numerical experiments and their applications|
Core-collapse supernovae are flamboyant explosions at death of massive stars.
They control the circulation of matter in the universe, and inevitably they
affect or are affected by a lot of astrophysical objects, such as supernova remnants, neutron stars, black holes, interplanetary disks and stars. The central engine of the explosion, however, remains in mystery. Elaborate numerical experiments try to uncover that. Stimulated by such precise simulations, phenomenological approaches are recently developed.In this seminar, I introduce the status of the supernova simulations and broaden applications of them.

:&aname(long0420){4/20}; Yuki Tanaka (NAOJ CfCA) Magnetically Driven Wind from Hot Gaseous Planets|
Several transit observations in the UV band have been suggested that hot Jupiters have high-temperature hydrogen upper atmospheres, and the existence of a large amount of atmospheric escape from the upper atmospheres. For example, a mass-loss rate from the hot Jupiter HD 209458b is estimated to be at least 10^10 g/s. It is thought that heating by the XUV radiation from central stars is the main mechanism to drive the atmospheric escape, but a driving mechanism of atmospheric escape that includes planetary magnetic fields has not been investigated so far. Here I propose a new mechanism in which the atmospheric escape is driven by the dissipation of magnetohydrodynamic (MHD) waves. I performed MHD simulations and show that the dissipation of MHD waves in the upper atmosphere can drive a large amount of atmospheric escape and also can heat up the upper atmosphere. I also discuss parameter dependence of the mass-loss rate and atmospheric structures.

:&aname(long0425){4/25}; Kohei Inayoshi (Columbia University) Hyper-Eddington accretion flows onto massive black holes|
How fast can black holes (BHs) grow?  The existence of bright quasars at high-redshift provides a challenging puzzle about the origin of supermassive BHs. To form such massive objects within a billion year, rapid growth of seed BHs is required. We study very-high rate, spherically symmetric accretion flows onto massive BHs embedded in dense metal-poor clouds. We find solutions from outside the Bondi radius at hyper-Eddington rates, unimpeded by radiation feedback. Accretion rates in this regime are steady, and larger than 5000 L_Edd/c^2. At lower rates, the accretion is episodic due to radiative feedback and the average rate is below the Eddington rate. The hyper-Eddington accretion solution is maintained as long as the emergent luminosity is limited to < (10-30) L_Edd because of photon trapping due to electron scattering. We apply our result to the rapid formation of massive BHs in protogalaxies. Once a seed BH forms at the center of the galaxy, it can grow to a maximum ~ 10^5 Msun via gas accretion independent of the initial BH mass.

:&aname(long0427){4/27}; Tetsuo Taki (NAOJ CfCA) Toward formation of rocky planetesimals: dust and gas density evolution at a local structure of protoplanetary disks|
The radial drift barrier is one of the most serious problem in the planetesimal formation process. We focus on a local disk structure called "radial pressure bump (Whipple, 1972; Haghighipour & Boss, 2003a, b)”. When a protoplanetary disk has the radial pressure bump, dust particles are trapped at a point where gas pressure is radially maximized. We investigate simultaneous evolution of dust and gas density profiles at a radial pressure bump. We find that the bump structure is flattened by a drag force from dust onto gas when the dust-to-gas mass ratio reaches ~1. Although the pressure bump is a favorable place for streaming instability (SI; Youdin & Goodman, 2005), the flattened bump structure inhibits SI from forming large particle clumps corresponding to 100-1000 km sized bodies, which has been previously proposed. If SI occurs there, the dust clumps formed would be 10-100 times smaller, that is, of about 1 - 100 km.

:&aname(long0511){5/11}; Masahiro Ogihara (NAOJ DTA) Formation of close-in super-Earths|
Recent observations of exoplanets have revealed a large number of
close-in low-mass planets (or close-in super-Earths). As of April
2016, 351 systems harbor 877 close-in super-Earths. We can discuss the
origin of these planets by comparing observed orbital distributions
with results of numerical simulations of planet formation. In this
talk, I will introduce our recent papers on formation of close-in
super-Earths (Ogihara et al. 2015, A&A, 578; Ogihara et al. 2015,
A&AL, 584). I will also show some preliminary results of ongoing
projects.

:&aname(long0518){5/18}; Takashi Moriya (NAOJ DTA) Superluminous supernovae and their origins|
Superluminous supernovae (SLSNe) are newly recognized class of core-collapse supernovae (SNe). Their existence is realized only about a decade ago. They are more than 10 times brighter than other core-collapse SNe. The reasons why they can become very bright are still not understood well. It is currently known that there are two distinct spectral types in SLSNe, namely, Type II (those with hydrogen features) and Type I (those without them). Type II SLSNe show narrow spectral features which are likely from dense circumstellar media surrounding the SN ejecta. I will present the numerical modeling of the collision between SN ejecta and dense circumstellar media and show that the interaction between SN ejecta and dense circumstellar media can indeed explain Type II SLSNe. Origins of Type I SLSNe are more mysterious. I will discuss several works of mine related to the luminosity source of Type I SLSNe. I will especially focus on the Type I SLSN iPTF13ehe which did not show hydrogen features at the beginning but started to show them one year after its luminosity peak. I suggest that the delayed hydrogen features may be an evidence of Type I SLSN progenitors evolving in close massive binary systems.

:&aname(long0525){5/25}; Yukari Ohtani (NAOJ CfCA) title|
Abstract

// 6/15
:&aname(long0615){6/15}; Makoto Takamoto (Tokyo University) Relativistic Magnetohydrodynamic turbulence in Poynting-Dominated Plasmas and its effects on Current Sheet Dynamics|
Many astrophysical phenomena are considered that the ambient plasma is very high-Reynolds number flows, and should be in a turbulent state. In particular, many high energy astrophysical phenomena are also believed to be in high-sigma state, that is, the plasma is in a Poynting-dominated state. To investigate such phenomena, we need a theory of turbulence of relativistic magnetohydrodynamics (RMHD) with relativistically strong background magnetic field. However, there are very few study of relativistic turbulence, and many properties are still unknown.
In this seminar, we report on our recent findings of the RMHD turbulence in a Poynting-dominated plasma, in particular, effects of compression mode. We performed a series of 3-dimensional RMHD simulations with decaying trans-Alfvenic turbulence. We found that the generation of compressible mode shows different behavior from non-relativistic case, such as an increase of compression mode power with back ground sigma parameter and effects from shock waves. We also discuss the turbulent effects on magnetic reconnection.

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