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Colloquium

Last-modified: 2017-04-26 () 17:08:15 (1d)
Top / Colloquium

2017

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䤤碌ϰʲΥ෸ޤǤꤤޤ_AT_@ѹƤˡ

  • takiwaki.tomoya_AT_nao.ac.jp
  • Ҳ ϲ akimasa.kataoka_AT_nao.ac.jp
  • Kenneth Wong ken.wong ATM nao.ac.jp
  • ⶶ Ƿ takahashi ATM cfca.jp
  • ʿ ͪ yutaka.hirai ATM nao.ac.jp

Schedule & History

2010ǯ 2011ǯ 2012ǯ 2013ǯ 2014ǯ 2015ǯ 2016ǯ

DateSpeakerTitlePlace/Timeremarks
4/5all internal membersself-introductionConference room, Cosmos Lodge / 13:30
4/12Shing Chi Leung (Kavli IPMU)Nucleosynthesis of Type Ia supernovaeConference room, Cosmos Lodge / 13:30
4/17Toshihiko Kawano (LANL/Tokyo Tech)beta-delayed neutron emission and fission for r-process nucleosynthesisConference room, Cosmos Lodge / 13:30
4/19Masaki Yamaguchi (U. Tokyo)The number of black hole-star binaries discovered by the astrometric satellite, GaiaConference room, Cosmos Lodge / 13:30
4/26Tomohisa Kawashima (NAOJ DTA)Radiation hydrodynamic simulations of super-critical accretion columns onto neutron stars in ULX-pulsarsConference room, Cosmos Lodge / 13:30
5/08Jonathan C. Tan (University of Florida)Inside-Out Planet FormationConference room, Cosmos Lodge / 13:30
5/10Shinpei Shibata (Yamagata University)Physics of The Rotation Powered PulsarConference room, Cosmos Lodge / 13:30
5/17Tomohiro Ono (Kyoto University)Large-scale Gas Vortex Formed by the Rossby Wave InstabilityConference room, Cosmos Lodge / 13:30
5/24Naonori Sugiyama (IPMU)TBAConference room, Cosmos Lodge / 13:30
5/31Shogo Ishikawa (NAOJ CfCA)TBAConference room, Cosmos Lodge / 13:30
6/7Tomoya Kinugawa (U. Tokyo)TBAConference room, Cosmos Lodge / 13:30
6/28Masanobu Kunitomo (Nagoya University)Revisiting the pre-main sequence evolution of low-mass stars: Importance of accretion and deuterium abundanceConference room, Cosmos Lodge / 13:30
7/19Shinsuke Takasao (Nagoya University)MHD Simulations of Accretion onto Star from Surrounding DiskConference room, Cosmos Lodge / 13:30
--/--Shoko Oshigami (NAOJ CfCA)Mare volcanism: Reinterpretation based on Kaguya Lunar Radar Sounder dataConference room, Cosmos Lodge / 13:30

Confirmed speakers

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 theorys 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.
--/-- 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.