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Colloquium のバックアップ(No.31)


理論コロキウム2016

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

Schedule & History

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

DateSpeakerTitlePlace/Timeremarks
4/6all internal membersself-introductionConference room, Cosmos Lodge / 13:30
4/13Tomoya Takiwaki (NAOJ DTA)A Clockwork Supernova: precision numerical experiments and their applicationsConference room, Cosmos Lodge / 13:30
4/20Yuki Tanaka (NAOJ CfCA)Magnetically Driven Wind from Hot Gaseous PlanetsConference room, Cosmos Lodge / 13:30
4/25Kohei Inayoshi (Columbia University)Hyper-Eddington accretion flows onto massive black holesLecture Room/ 13:30
4/27Tetsuo Taki (NAOJ CfCA)Toward formation of rocky planetesimals: dust and gas density evolution at a local structure of protoplanetary disksConference room, Cosmos Lodge / 13:30
5/11Masahiro Ogihara (NAOJ DTA)Formation of close-in super-EarthsConference room, Cosmos Lodge / 13:30
5/18Takashi Moriya (NAOJ DTA)Superluminous supernovae and their originsLarge seminar room / 13:30
5/25Yukari Ohtani (NAOJ CfCA)Study of relation between emission of supernova shock breakout and central engine activityConference room, Cosmos Lodge / 13:30
6/1Shogo Tachibana (Hokkaido University)Timing of gas clearing of the protosolar disk: Constraints from 129I-129Xe ages of solar-wind-rich meteoritesConference room, Cosmos Lodge / 13:30
6/8Alessandro Sonnenfeld (IPMU)Dark matter in early-type galaxies: a lensing viewConference room, Cosmos Lodge / 13:30
6/15Makoto Takamoto (University of Tokyo)Relativistic Magnetohydrodynamic turbulence in Poynting-Dominated Plasmas and its effects on Current Sheet DynamicsConference room, Cosmos Lodge / 13:30
6/22Takahiro Sumi (Osaka University)Microlensing exoplanet search toward the solar system analogConference room, Cosmos Lodge / 13:30
6/29Carmen Adriana Martínez Barbosa (Leiden Observatory, University of Leiden)Tracing the journey of the Sun and the solar siblings through the Milky WayConference room, Cosmos Lodge / 13:30
7/6Shota Kisaka (Aoyama Gakuin University)Engine-powered macronovaeConference room, Cosmos Lodge / 13:30
7/13Tomoaki Matsumoto (Hosei University)Theoretical Models of Protostellar Binary and Multiple Systems with AMR Simulations.Conference room, Cosmos Lodge / 13:30
8/24Hui Jiang (Shanghai Maritime University)Local Nuclear Mass RelationsConference room, Cosmos Lodge / 10:30
8/31Sherry Suyu (MPA)Shedding Light on the Dark Cosmos through Gravitational LensingLarge Seminar Room / 13:30
9/21Kazunori Akiyama (MIT)TBAConference room, Cosmos Lodge / 13:30
10/5Toshio Fukushima (NAOJ)Numerical integration of gravitational field for general three-dimensional objects and its application to gravitational study of grand design spiral arm structureConference room, Cosmos Lodge / 13:30
10/12Annop Wongwathanarat (RIKEN)TBAConference room, Cosmos Lodge / 13:30
10/14TBA (TBA)TBAConference room, Cosmos Lodge / 13:30
10/19Naoki Yamamoto(Keio University)TBAConference room, Cosmos Lodge / 13:30
10/26Chit Hong Yam (JAXA)TBATBA / 13:30
11/9Hisasi Hayakawa(Kyoto University)TBAConference room, Cosmos Lodge / 13:30
11/22Shota Shibagaki(NAOJ)TBAConference room, Cosmos Lodge / 13:30
12/14Shunsuke Hozumi (Shiga University)TBAConference room, Cosmos Lodge / 13:30

Confirmed speakers

Abstract

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.
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.
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.
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.
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.
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.
5/25 Yukari Ohtani (NAOJ CfCA) Study of relation between emission of supernova shock breakout and central engine activity
Shock breakout radiation originate as thermal emission from the shock passing through the outer layer of the star. It can provide the first information on how supernova explodes, no matter how relativistic the explosion is. There have been an question about the relativistic jet associated with a hypernova, of which explosion energy is ten times higher than that of an ordinary core-collapse supernova. The question is, how the central engine of the jet works. In order to obtain information on the central engine activity, it might be worth studying the emission properties of ultra-relativistic shock propagating into the dense circumstellar matter (CSM). For example, influence of bulk-Compton scattering on the spectrum can be a powerful indicator of the shock evolution, but there have been no theoretical study on that. In this talk, I will introduce our numerical study on the relationship between the behavior of an ultra-relativistic shock and the spectral properties of shock breakout emission. Using a Monte-Carlo method, we calculate the temporal spectral evolution of ultra-relativistic shock breakout in the CSM. We found that if the shock velocity monotonically decreases with time, photons with relatively high energies tend to appear fast. That is because the bulk kinetic energy of the shocked matter decreases. On the other hand, if the shock velocity increases with time, there are only slight changes in the spectrum. Therefore, in principle, it might be possible to obtain information on the activity of the jet central engine from the observable properties of ultra-relativistic shock breakout.
6/1 Shogo Tachibana (Hokkaido University) Timing of gas clearing of the protosolar disk: Constraints from 129I-129Xe ages of solar-wind-rich meteorites
Planets in the solar system and extrasolar planets form in protoplanetary disks, which are the natural outcome of the star formation. The protosolar gas disk also dispersed after the formation of Jupiter and Saturn, resulting in the insufficient gas accretion onto later-formed Uranus and Neptune cores. However, there has been no chronological constraint when the gas disk dispersed in the solar system. Here we found that solar-wind-rich portions of gas-rich chondrite breccias are about 10 million years younger than the oldest solar system solid objects using a 129I-129Xe relative chronometer. The solar-wind gas implantation into asteroids must have occurred in the absence of disk gas, and thus the disk gas was cleared out completely ~10 million years after the first solid formation. This could also be the first direct constraint on the timing of the onset of Jupiter and Saturn formation as ~3 million years after the first solid formation.
6/8 Alessandro Sonnenfeld (IPMU) Dark matter in early-type galaxies: a lensing view
Dark matter halos play a crucial role in the formation and evolution of galaxies but observational constraints on the distribution of dark matter are currently very poor.Gravitational lensing is a very powerful tool for measuring galaxy masses at cosmological distances and provides a unique opportunity for probing the distribution of dark matter in the most massive galaxies. By statistically combining the lensing signal from a large set of galaxies we explored how the average dark matter distribution correlates with the properties of the baryonic component. Strong lensing constraints reveal an anticorrelation between galaxy size and dark matter mass enclosed within 5kpc. At larger scales, probed by weak lensing, we observe a positive correlation between halo mass and the velocity dispersion of the central galaxy, at fixed stellar mass. These results could have a significant impact on our understanding of the formation and evolution of massive galaxies.
6/15 Makoto Takamoto (University of Tokyo) 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.
6/22 Takahiro Sumi (Osaka University) Microlensing exoplanet search toward the solar system analog
Although thousands of exoplanets have been found by various methods, not many solar system planets analogs have been detected. Some Jupiter and Saturn analogs and a few Earth-like plants have been found only very recently. Gravitational microlensing has an unique sensitivity to exoplanets outside the snow-line down to the Earth-mass, where the planetary formation is very active. The MOA-II and OGLE-IV carries out microlensing exoplanet search toward the Galactic Bulge in New Zealand and Chile, respectively. These surveys are detecting various kinds of systems, including the Jupiter-Saturn analog, the Neptune analog and the 2-Earth mass planet at 1AU around one of the binary stars. The Wide Field Infrared Survey Telescope (WFIRST) is the NASA's future large space mission, which is scheduled to be launched in 2024. The exoplanet microlensing program is one of the primary science of WFIRST. WFIRST will find about 3000 bound planets and 2000 unbound planets by the high precision continuous survey with 15 min. cadence, which is sensitive to all the solar system analogs except the mercury. WFIRST can complete the statistical census of planetary systems in the Galaxy, from the outer habitable zone to the outside of the snow-line and gravitationally unbound planets – a discovery space inaccessible to other exoplanet detection techniques.
6/29 Carmen Adriana Martínez Barbosa (Leiden Observatory, University of Leiden) Tracing the journey of the Sun and the solar siblings through the Milky Way
The products of radioactive elements found in the meteorite fossil record and the high eccentricities of objects located in the outer regions of the Solar System, suggest that the Sun was born in an open cluster 4.6 Gyr ago. Such an open cluster however, was quickly destroyed by the intense gravitational field of the Galaxy. As a conse- quence, the stars that were born together with the Sun, the so-called solar siblings, might be currently dispersed all over the Galactic disk.
In this talk I will explain how open cluster simulations can help us in predicting the current phase-space coordinates of the solar siblings. These simulations include the gravitational forces within the cluster, the effects of stellar evolution on the cluster population and the gravitational force due to the Milky Way. The result of these sim- ulations will serve as a guide to search for solar siblings in future surveys such as the Gaia mission and GALAH. The identification of solar siblings is of crucial importance to understand the environment where the Solar system was formed and the place in the Galaxy where the Sun was born.
7/06 Shota Kisaka (Aoyama Gakuin University) Engine-powered macronovae
In 2015, a gravitational-wave (GW) signal was directly detected from a merger of a binary black hole (BH) for the first time. GW signals are expected to be generated not only by mergers of binary BHs, but also by mergers of neutron star (NS) binaries (NS-NS and BH-NS binaries). NS binary mergers may also power bright electromagnetic (EM) signals, because the ejection of normal matter during mergers is thought to be responsible. EM counterparts have been focused on to maximize the scientific return from the detection of GWs. One of the most promising EM signatures are macronovae (or kilonovae): approximately isotropic emissions from heated merger ejecta. Although the r-process radioactivity is widely discussed as an energy source, it requires a huge mass of ejecta from a NS binary merger to explain the observed macronova candidates. As an alternative, we propose that macronovae are energized by the central engine, i.e., a BH or NS, and the injected energy is emitted. The engine model allows a wider parameter range, especially smaller ejecta mass than the r-process model. We also discuss the implications for the engine-powered model for the search of EM counterparts to GWs.
7/13 Tomoaki Matsumoto (Hosei University) Theoretical Models of Protostellar Binary and Multiple Systems with AMR Simulations.
We present theoretical models for protostellar binary and multiple systems based on the high-resolution numerical simulation with an adaptive mesh refinement (AMR) code, SFUMATO. The recent ALMA observations reveal early phases of the binary and multiple star formation with high spatial resolutions. The observations should be compared with theoretical models with also high spatial resolutions. We present two theoretical models for (1) a high density molecular cloud core, MC27, and (2) a protobinary system, L1551 NE. For the model for MC27, we performed numerical simulations for gravitational collapse of a turbulent cloud core. The cloud core exhibits fragmentation during the collapse, and dynamical interaction between the fragments produces an arc-like structure, which is one of the prominent structures observed by ALMA. The effects of the magnetic field are also discussed with MHD simulations. For the model for L1551 NE, we performed numerical simulations of gas accretion onto protobinary. The simulations exhibit asymmetry of circumbinary disks. Such asymmetry was also found by ALMA in the circumbinary disk of L1551 NE.
8/24 Hui Jiang (Shanghai Maritime University) Local Nuclear Mass Relations
The masses are the basic properties of atomic nuclei. In this talk, we will discuss the Garvey-Kelson mass relations as one of the best example schemes of local nuclear mass relations and, report in particular our recent results of researches which we have carried out in the Shanghai Jiao Tong University. The essential point is how to use and improve the Garvey-Kelson relations. We plan to apply our result to explosive nucleosynthesis in SNe.
8/31 Sherry Suyu (MPA) Shedding Light on the Dark Cosmos through Gravitational Lensing
Gravitational lensing provides powerful means to study dark energy and dark matter in the Universe. In particular, strong lens systems with measured time delays between the multiple images can be used to determine the "time-delay distance" to the lens, which is primarily sensitive to the Hubble constant. Measuring the Hubble constant is crucial for inferring properties of dark energy, spatial curvature of the Universe and neutrino physics. I will describe the ingredients and newly developed techniques for measuring accurately time-delay distances with a realistic account of systematic uncertainties. A program initiated to measure the Hubble constant to <3.5% in precision from gravitational lens time delays is in progress, and I will present the latest results and their implications. Current and upcoming imaging surveys will contain thousands of new time-delay lenses, and I will describe ongoing efforts to find these objects. An exciting discovery is the first strongly lensed supernova, which has offered a rare opportunity to perform a true blind test of model predictions. I will describe the bright prospects of using gravitational lens time delays as an independent and competitive cosmological probe.
10/5 Toshio Fukushima (NAOJ) Numerical integration of gravitational field for general three-dimensional objects and its application to gravitational study of grand design spiral arm structure
We present a method to integrate the gravitational field for general three-dimensional objects. By adopting the spherical polar coordinates centered at the evaluation point as the integration variables, we numerically compute the volume integral representation of the gravitational potential and of the acceleration vector. The variable transformation completely removes the algebraic singularities of the original integrals. The comparison with exact solutions reveals around 15 digits accuracy of the new method. Meanwhile, the 6 digit accuracy of the integrated gravitational field is realized by around $10^6$ evaluations of the integrand per evaluation point, which costs at most a few seconds at a PC with Intel Core i7-4600U CPU running at 2.10 GHz clock. By using the new method, we show the gravitational field of a grand design spiral arm structure as an example. The computed gravitational field shows not only spiral shaped details but also a global feature composed of a thick oblate spheroid and a thin disc. The developed method is directly applicable to the electromagnetic field computation by means of Coulomb's law, the Biot-Savart law, and their retarded extensions. Sample {\sc fortran} 90 programs and test results are electronically available. (Ref. T. Fukushima 2016, MNRAS, doi:10.1093/mnras/stw2078)