Colloquium のバックアップ(No.8)

理論コロキウム2017 †

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
片岡章雅 akimasa.kataoka_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

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Schedule & History †

2010年度 2011年度 2012年度 2013年度 2014年度 2015年度 2016年度

Date	Speaker	Title	Place/Time	remarks
4/5	all internal members	self-introduction	Conference room, Cosmos Lodge / 13:30
4/12	Shing Chi Leung (Kavli IPMU)	Nucleosynthesis of Type Ia supernovae	Conference room, Cosmos Lodge / 13:30
4/17	Toshihiko Kawano (LANL/Tokyo Tech)	beta-delayed neutron emission and fission for r-process nucleosynthesis	Conference room, Cosmos Lodge / 13:30
4/19	Masaki Yamaguchi (U. Tokyo)	The number of black hole-star binaries discovered by the astrometric satellite, Gaia	Conference room, Cosmos Lodge / 13:30
4/26	Tomohisa Kawashima (NAOJ DTA)	Radiation hydrodynamic simulations of super-critical accretion columns onto neutron stars in ULX-pulsars	Conference room, Cosmos Lodge / 13:30
5/08	Jonathan C. Tan (University of Florida)	Inside-Out Planet Formation	Conference room, Cosmos Lodge / 13:30
5/10	Shinpei Shibata (Yamagata University)	Physics of The Rotation Powered Pulsar	Conference room, Cosmos Lodge / 13:30
5/17	Tomohiro Ono (Kyoto University)	Large-scale Gas Vortex Formed by the Rossby Wave Instability	Conference room, Cosmos Lodge / 13:30
5/24	Naonori Sugiyama (IPMU)	TBA	Conference room, Cosmos Lodge / 13:30
5/31	Shogo Ishikawa (NAOJ CfCA)	TBA	Conference room, Cosmos Lodge / 13:30
6/7	Tomoya Kinugawa (U. Tokyo)	Compact binary remnants from first stars for the gravitational wave source	Conference room, Cosmos Lodge / 13:30
6/12	Yamaç Pehlivan Deliduman (Mimar Sinan University)	TBA	Conference room, Cosmos Lodge / 13:30
6/14	Cemsinan Deliduman (Mimar Sinan University)	TBA	Rinkoh room / 13:30
6/28	Masanobu Kunitomo (Nagoya University)	Revisiting the pre-main sequence evolution of low-mass stars: Importance of accretion and deuterium abundance	Conference room, Cosmos Lodge / 13:30
7/19	Shinsuke Takasao (Nagoya University)	MHD Simulations of Accretion onto Star from Surrounding Disk	Conference room, Cosmos Lodge / 13:30
--/--	Shoko Oshigami (NAOJ CfCA)	Mare volcanism: Reinterpretation based on Kaguya Lunar Radar Sounder data	Conference room, Cosmos Lodge / 13:30

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Confirmed speakers †

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Abstract †

4/12 Shing Chi Leung (Kavli IPMU) Nucleosynthesis of Type Ia supernovae: Type Ia supernovae (SNe Ia) are an important class of astrophysical objects. They are the standard candles of the universe and the major sources of iron-peak elements. It is known to be the explosion of a carbon-oxygen white dwarf by thermonuclear runaways. However, many theoretical uncertainties still persist, for example whether the progenitor of SNe Ia belongs to single degenerate or double degenerate scenario. Furthermore, the diversity in observations, such as the subclasses of Type Iax or super-luminous SNe Ia, suggests that the standard picture using the explosion of a Chandrasekhar mass white dwarf is insufficient to explain the variety of the observed SNe Ia. To resolve these, a systematic understanding in SNe Ia nucleosynthesis becomes necessary. In this present, I shall present hydrodynamics and nucleosynthesis results of multi-dimensional models for the explosion phase of SNe Ia. We explore the effects of model parameters on the explosion energetic and its chemical production. The influences of our SNe Ia models to galactic chemical evolution are discussed. I also present constraints on the progenitor properties of some recently observed SNe Ia and their remnants.

4/17 Toshihiko Kawano (LANL/Tokyo Tech) beta-delayed neutron emission and fission for r-process nucleosynthesis: We give a brief summary of our recent development of nuclear reaction theories with a particular focus on nuclear data production for the r-process nucleosynthesis. The topics include calculations of the beta-delayed process for neutron-rich nuclei, where several neutrons can be emitted, and eventually fission may take place as well. Our recent studies on fission itself are also given.

4/19 Masaki Yamaguchi (U. Tokyo) The number of black hole-star binaries discovered by the astrometric satellite, Gaia: Although it is believed that there are 10^8-9 stellar mass black holes (BH) in Milky Way, until now only ~60 BHs have been discovered. Moreover, masses of only a dozen BHs of them are constrained. By discovering more BHs and estimating their masses, we would obtain the mass distribution of BHs with a higher confidence level. This distribution is expected to constrain a theoretical model of the supernova explosion in which a BH is produced as a remnant. Gaia is now operated and have a capability to detect binaries with an unseen companion, such as a BH or a neutron star. Gaia performs a high-precision astrometry with the optical band (0.3-1.0um), and surveys a whole sky, where main observational targets are stars. If a target star has an unseen companion, it should show an elliptical motion on the celestial sphere. Gaia can confirm the companion by detecting such motion. Moreover, this elliptical motion leads to all orbital elements, which enables us to estimate the mass of companion. If this mass is larger than 3 solar masses, we can confirm the companion as a BH. In my talk, I will show how many BHs can be detected by such method with Gaia. Considering the binary evolution, we obtain the number of detectable BHs, ~600, for main sequence targets. This means that Gaia can discover the order of one thousand BHs whose masses can be found, although we know only a dozen such BHs now. We conclude that the astrometric observation for binaries is very powerful method for finding BHs.

4/26 Tomohisa Kawashima (NAOJ) Radiation hydrodynamic simulations of super-critical accretion columns onto neutron stars in ULX-pulsars: Ultraluminous X-ray sources are off-centered, extragalactic X-ray sources with luminosities exceeding the Eddington limit for stellar-mass black holes. After the recent discovery of pulsed X-ray emissions in three ULXs, it is widely thought that some ULXs are powered by super-critical column accretion onto neutron stars. The mechanism of super-critical column accretion is, however, still poorly understood. We have, therefore, carried out two-dimensional radiation hydrodynamic simulations of super-critical accretion columns onto neutron stars, and have found that the super-critical accretion can be realized because the most photons escape from the side wall of accretion columns (i.e., the radiation field is anisotropic in the accretion columns). The simulated accretion columns are luminous enough to be consistent with the observed ULX-pulsars.

5/08 Jonathan C. Tan (University of Florida) Inside-Out Planet Formation: The Kepler-discovered systems with tightly-packed inner planets (STIPs), typically with several planets of Earth to super-Earth masses on well-aligned, sub-AU orbits may host the most common type of planets in the Galaxy. They pose a great challenge for planet formation theories, which fall into two broad classes: (1) formation further out followed by migration; (2) formation in situ from a disk of gas and planetesimals. I review the pros and cons of these classes, before focusing on a new theory of sequential in situ formation from the inside-out via creation of successive gravitationally unstable rings fed from a continuous stream of small (~cm-m size) "pebbles," drifting inward via gas drag. Pebbles first collect at the pressure trap associated with the transition from a magnetorotational instability (MRI)-inactive ("dead zone") region to an inner MRI-active zone. A pebble ring builds up until it either becomes gravitationally unstable to form an Earth to super-Earth-mass planet directly or induces gradual planet formation via core accretion. The planet continues to accrete until it becomes massive enough to isolate itself from the accretion flow via gap opening. The process repeats with a new pebble ring gathering at the new pressure maximum associated with the retreating dead-zone boundary. I discuss the theory’s predictions for planetary masses, relative mass scalings with orbital radius, and minimum orbital separations, and their comparison with observed systems. Finally I speculate about potential causes of diversity of planetary system architectures, i.e. STIPs versus Solar System analogs.

5/10 Shinpei Shibata (Yamagata University) Physics of The Rotation Powered Pulsar: I review physics of the rotation powered pulsars with special interest of how the energy and angular momentum are emitted from the system. I will mention briefly an recent observational result that torque on the neutron stars varies with various time scales. This talk is given in Japanese.

5/17 Tomohiro Ono (Kyoto University): Large-scale Gas Vortex Formed by the Rossby Wave Instability| Large-scale gas vortexes induced by the Rossby wave instability (RWI) are one of the plausible explanations of the lopsided structures recently observed in several protoplanetary disks. For comparison with the observations, it is important to investigate quantitatively the properties of the vortexes formed by the RWI. However, our knowledge on the properties and outcomes of the RWI has been limited until recent years. We have studied the RWI with linear stability analyses and hydrodynamical simulations using the Athena++ code. As a result of the linear stability analyses, we show that the RWI is one of the shear instabilities which are explained by the interaction between two Rossby waves. We also derive the critical condition for the onset of the RWI in semi-analytic form. From the numerical simulations, we investigate the properties of the vortexes formed by the RWI and discuss possible observational predictions. In my talk, I will present our three results on the RWI: (1) the physical mechanism, (2) the critical condition for the onset and (3) the properties of the vortexes.

6/7 Tomoya Kinugawa (U. Tokyo) compact binary remnants from first stars for the gravitational wave source: Using our population synthesis code, we found that the typical chirp mass of binary black holes (BH-BHs) whose origin is the first star (Pop III) is ~30 Msun. This result predicted the gravitational wave events like GW150914 and LIGO paper said "recently predicted BBH total masses agree astonishingly well with GW150914 and can have sufficiently long merger times to occur in the nearby universe (Kinugawa et al. 2014)" (Abbot et al. ApJL 818,22 (2016)). Thus, the compact binary remnants of the first stars are interesting targets of LIGO,VIRGO and KAGRA.Nakano, Tanaka & Nakamura 2015 show that if S/N of QNM is larger than 35, we can confirm or refute the General Relativity more than 5 sigma level. In our standard model, the detection rate of Pop III BH-BHs whose S/N is larger than 35 is 3.2 events/yr (SFR_p/(10^{-2.5}Msun/yr/Mpc^3))*([f_b/(1+f_b)]/0.33)* Err_sys. Thus, there is a good chance to check whether GR is correct or not in the strong gravity region. Furthermore, the Pop III binaries become not only BH-BH but also NS-BH. We found Pop III NS-BH merger rate is ~ 1 events/Gpc^3 and the chirp mass of Pop III NS-BH is more massive than that of Pop I and II. Therefore, we might get information of Pop III stars from massive BH-BHs and NS-BHs.

6/28 Masanobu Kunitomo (Nagoya University): Revisiting the pre-main sequence evolution of low-mass stars: Importance of accretion and deuterium| Recent theoretical work has shown that the pre-main sequence (PMS) evolution of stars is much more complex than previously envisioned: Instead of the traditional one-dimensional solution of the contraction of a spherically symmetric gaseous envelope, protostars grow from the first formation of a small seed and subsequent accretion of material. This material is shocked, accretion may be episodic and not necessarily symmetrical, thereby affecting the energy deposited inside the star and its interior structure. Given this new framework, we confirm the findings of previous works (e.g., Baraffe et al. 2009, 2012, Hosokawa et al. 2011) that the evolution changes significantly with the amount of energy that is lost during accretion. We find that deuterium burning also regulates the PMS evolution. In the low-entropy accretion, the evolutionary tracks in the Hertzsprung-Russell diagram are significantly different from the classical ones and sensitive to the deuterium content. Our results agree with previous work that the variation of heat injection can be the solution of luminosity spread problem of PMS stars and show the importance of the deuterium content. We also discuss the internal structure evolution of young stars and the impact on the stellar surface composition.

--/-- Shoko Oshigami (NAOJ CfCA) Mare volcanism: Reinterpretation based on Kaguya Lunar Radar Sounder data: The Lunar Radar Sounder (LRS) onboard Kaguya (SELENE) detected widespread horizontal reflectors under some nearside maria. Previous studies estimated that the depths of the subsurface reflectors were up to several hundreds of meters and suggested that the reflectors were interfaces between mare basalt units. The comparison between the reflectors detected in the LRS data and surface age maps indicating the formation age of each basalt unit allows us to discuss the lower limit volume of each basalt unit and its space and time variation. We estimated volumes of basalt units in the ages of 2.7 to 3.8 Ga in the nearside maria. The lower limit volumes of the geologic units estimated in this study were on the order of 10^3 to 10^4 km^3. This volume range is consistent with the total amount of erupted lava flows derived from numerical simulations of thermal erosion models of lunar sinuous rille formation and is also comparable to the average flow volumes of continental flood basalt units formed after the Paleozoic and calculated flow volumes of Archean komatiite flows on the Earth. The lower limits of average eruption rates estimated from the unit volumes were on the order of 10 ^5 to 10^ 3 km^3/yr. The estimated volumes of the geologic mare units and average eruption rate showed clear positive correlations with their ages within the same mare basin, while they vary among different maria compared within the same age range. This talk is given in Japanese.