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Colloquium2016

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2016

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䤤碌ϰʲΥ෸ޤǤꤤޤ_AT_@ѹƤˡ

  • takiwaki.tomoya_AT_nao.ac.jp
  • 鲰 takashi.moriya_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

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)Interstellar Scintillation and Radio Counterpart of the FRBsConference room, Cosmos Lodge / 13:30
9/23Akimasa Kataoka (Heidelberg University)Millimeter polarization of protoplanetary disks due to dust scatteringConference room, Cosmos Lodge / 11:00Friday
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)Linking core-collapse simulations with observationsConference room, Cosmos Lodge / 13:30
10/14Yiping Shu (the National Astronomical Observatories, Chinese Academy of Sciences)The BOSS Emission-Line Lens Survey: Strong Lensing of Ly Emitters by Individual GalaxiesConference room, Cosmos Lodge / 13:30Friday
10/19Naoki Yamamoto (Keio University)Chirality and AstrophysicsConference room, Cosmos Lodge / 13:30
10/26Chit Hong Yam (JAXA)Space Missions and Modern AstronomyConference room, Cosmos Lodge / 13:30
11/2Sergei Blinnikov (ITEP)Superluminous Supernovae: Current Status of ResearchConference room, Cosmos Lodge / 13:30
11/9Hisasi Hayakawa (Kyoto University)Historical Solar Activity before Telescopic Observations-- A New Perspective by Historical Documents --Rinkoh seminar room / 13:30
12/9Manos Chatzopoulos (Louisiana State University)Pre-supernova Convection in Massive StarsConference room, Cosmos Lodge / 13:30Friday
12/14Shunsuke Hozumi (Shiga University)Intrisic Properties of the Bars Formed by the Bar Instability in Flat Stellar DisksConference room, Cosmos Lodge / 13:30
1/6Federico García (Argentine Institute of Radio Astronomy)Probing generalized Kerr spacetimes through accretion disksConference room, Cosmos Lodge / 13:30Friday
1/19Alexander Heger (Monash Center for Astrophysics)Nucleosynthesis of the First StarsConference room, Cosmos Lodge / 13:30Thursday
1/25Fumi Egusa (NAOJ)Spiral Structure in Galactic DiskConference room, Cosmos Lodge / 13:30
2/1Ryo Tazaki (Kyoto University)Multiwavelength polarimetric properties of protoplanetary disksConference room, Cosmos Lodge / 13:30Wednesday
2/15Alexey Tolstov (Kavli IPMU)First stars, hypernovae, and superluminous supernovae: simulations of multicolor light curves and spectraConference room, Cosmos Lodge / 13:30
3/1Tatsuya Satsuka (Osaka University)Evolution of binary seeds in collapsing protostellar cloudRinkoh seminar room / 13:30Rinkoh seminar room!
3/8Benjamin Wu (NAOJ DTA)Star cluster formation triggered by giant molecular cloud collisionsConference 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.
9/21 Kazunori Akiyama (MIT) Interstellar Scintillation and Radio Counterpart of the FRBs
Fast radio bursts (FRBs) are one of the most intriguing sources, not only for astrophysical processes causing one of the most energetic but shortest bursts in the universe but also for their astronomical aspect of a unique probe for the intergalactic medium. Searches for counterparts of FRBs --- for instance, associated aftergrows are of significant importance for their localization. Refractive Interstellar scintillation is a critical consideration for searches for identification of associated aftergrows at radio wavelengths. The tenuous ionized interstellar medium along the line of sight can introduce rapid variability of compact radio sources such as active galactic nuclei (AGNs) on timescales comparable to potential aftergrows of the FRBs. Thus, it is quite essential to distinguish between associated aftergrows and rapidly variable scintillating sources close to FRBs. We have recently demonstrated a fundamental importance of the refractive scintillation for identification of the radio counterpart in a theoretical study on the effect of scintillation of the FRB 150418 (Akiyama & Johnson 2016, ApJL) that Keane et al. 2016 have recently discovered with a promising radio counterpart at 5.5 and 7.5 GHz --- a rapidly decaying source on timescales of ~ 6 days. The analytical theory of refractive scattering and our numerical simulations show that the reported observations on FRB 150418 are consistent with scintillating radio emission from the core of a radio-loud AGN having a brightness temperature of Tb ≳ 10^9 K, compatible with LLAGN and faint blazars. In this talk, I introduce FRBs and interstellar scintillation with our recent works on the FRB 150418. I also briefly discuss implications for future surveys of radio counterparts of compact objects such as FRBs and gravitational waves.
9/23 Akimasa Kataoka (Heidelberg University) Millimeter polarization of protoplanetary disks due to dust scattering
To measure if dust grains have grown to beyond millimeter sizes in protoplanetary disks, usually measurements of the spectral slope are used. However, the interpretation of millimeter spectral slopes in terms of grain size is unreliable. We have found a completely independent way to measure grain sizes in this size and wavelength regime: scattering polarization. If grains are grown to the comparable size of the wavelengths i.e., (sub)mm, dust grains scatter the thermal emission. The scattered emission is polarized by nature. The star itself is dark at millimeter wavelengths, the main source of the radiation is thermal dust emission itself. If a protoplanetary disk has a slight anisotropy such as lopsided or ring-shaped dust density distribution, the residual polarization is up to 2.5 %, which is observable with ALMA. Moreover, it explains measured polarization of emission from e.g. HL Tau. It turns out that this also allows for an independent measurement of the grain sizes; we have constrained the maximum grain sizes to be 150 µm. Also, we report our polarization observations with ALMA toward one of the brightest protoplanetary disks, which show an evidence of the self-scattering. This allows for a new probe of the grain growth in protoplanetary disks.
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)
10/12 Annop Wongwathanarat (RIKEN) Linking core-collapse simulations with observations
Core-collapse supernovae (CCSNe) are one of the most exciting astrophysical phenomena. The question of how massive stars die is a long-standing problem in theoretical astrophysics. Recently observations of young nearby CCSN remnants provide increasingly great details of the morphology and chemical composition of the remnants. Such information will help us to decipher the puzzle of the CCSN explosion mechanism. However, in order to understand a wide variety of properties of CCSN remnants long-time CCSN simulations must be performed. There is currently a missing link between simulations and observations because long-time CCSN simulations are computationally very demanding. In this talk, I will report results from state-of-the-art 3D long-time CCSN simulations, and present what we could learn about the explosion mechanism and the CCSN progenitor star from these results.
10/14 Yiping Shu (the National Astronomical Observatories, Chinese Academy of Sciences) The BOSS Emission-Line Lens Survey: Strong Lensing of Ly Emitters by Individual Galaxies
We present Hubble Space Telescope (HST) F606W-band imaging observations of 21 galaxy-Ly emitter lens candidates in the Baryon Oscillation Spectroscopic Survey (BOSS) Emission-Line Lens Survey (BELLS) for GALaxy-Ly EmitteR sYstems (BELLS GALLERY) survey. 17 systems are confirmed to be definite lenses with unambiguous evidence of multiple imaging. The lenses are primarily massive early-type galaxies (ETGs) at redshifts of approximately 0.55, while the lensed sources are Ly emitters (LAEs) at redshifts from 2 to 3. The HST imaging data are well fit by smooth lens models consisting of singular isothermal ellipsoids in an external shear field. The Einstein radii of the BELLS GALLERY lenses are on average 60% larger than those of the BELLS lenses because of the much higher source redshifts which will allow a detailed investigation of the radius evolution of the mass profile in ETGs. With the aid of the average ∼ 13 lensing magnification, the LAEs are resolved to comprise individual star-forming knots of a wide range of properties with characteristic sizes from less than 100 pc to several kpc, rest-frame far UV apparent AB magnitudes from 29.6 to 24.2, and typical projected separations of 500 pc to 2 kpc.
10/19 Naoki Yamamoto (Keio University) Chirality and Astrophysics
Elementary particles, such as electrons and neutrinos, possess the property of chirality. This microscopic property modifies the macroscopic hydrodynamic behavior and leads to unusual chiral transport phenomena in relativistic systems. We argue that these chiral effects are potentially important for the origin of magnetars and core-collapse supernova explosions.
10/26 Chit Hong Yam (JAXA) Space Missions and Modern Astronomy
In the past 50 years, there are over a hundred telescopes and astronomical devices launched to space and they have contributed in modern astronomy in various aspects. Space observation has two main advantages over ground-based telescopes: the absence of atmospheric disturbance and absorption. While the problem of atmospheric disturbance can be partially corrected by optical techniques, the observation of wavelengths absorbed by the atmosphere cannot be performed with ground-based telescopes. This talk presents the opportunities provided by space observatories and the challenges of designing and operating such missions. Basic orbital mechanics and spacecraft systems are introduced to explain how we can plan and operate a space mission to fulfill its scientific objectives. Past and future missions such as the Hubble Space Telescope, WMAP, SOHO, Kepler, LISA will be used as examples. Although space telescopes are much more expensive than ground-based telescopes, their values have been demonstrated in numerous important findings and will continue to help us answer some fundamental questions in astronomy, such as the origin of the universe, the formation and evolution of celestial objects and systems, and the possibility of extraterrestrial life.
11/2 Sergei Blinnikov (ITEP) Superluminous Supernovae: Current Status of Research
Many supernovae are discovered in last decade with peak luminosity one-two orders of magnitude higher than for normal supernovae of known types. They are called Superluminous supernovae: SLSNe. This is a challenge for theory, since even normal supernovae are not yet completely understood from the first principles. The models explaining those events with the minimum energy budget involve multiple ejections of mass in presupernova stars. The radiative shocks produced in collisions of those shells may provide the required power of light. This class of the models is refered to as "interacting'' supernovae. I concentrate on the non-trivial problems of this scenario for SLSNe: stability of the shells, on "bumps" in the light curves, and on the broad lines often observed in their spectra.
11/9 Hisasi Hayakawa (Kyoto University) Historical Solar Activity before Telescopic Observations -- A New Perspective by Historical Documents --
This presentation provides possibility and importance of historical documents for astronomical studies. Solar Activity is studied both on respects of long-term activity and extreme space events. We have 400-year data for sunspot drawings since Gallillei and 150-year data for flares since Carrington event. However, recent studies for the sun require longer time-scaled finding rare and extreme events such as "superflares", superflares, whose total enery of about 10^(33-38) erg, 10-10^6 times lager than that of the largest solar foares on the Sun and whose frequency is calculated once hundreds to thousand years. Historical documents can partially cover this shortage, recording low latitude auroras and naked-eye sunspots as proxies for solar activity. Thus, in this presentation, the presenter aims at introducing examples of aurora records in Carrington event in comparison with contemporary magnetic latitude of observational sites and showing further possibility of historical documents for astronomy. This approach casts a new perspectives for extreme events as large as or even larger than the Carrington event in our sun.
12/9 Manos Chatzopoulos (Louisiana State University) Pre-supernova Convection in Massive Stars
The interior of a massive star in the final years prior to core-collapse supernova is in a state of violent unrest. Vigorous convective shell burning of silicon, oxygen and carbon drives large scale plume motions that can interact with each other and significantly alter the structure of the progenitor star. Under such conditions the star departs from perfect hydrostatic equilibrium and spherical symmetry and may experience dynamical pulses that, in some cases, can lead to episodic mass-loss. I will present preliminary results from multidimensional simulations of convection in massive stars in the few seconds to hours preceding the supernova explosion. The proper, dynamical multidimensional treatment of convection will be bench-marked against parametrized one-dimensional mixing length theory predictions and the implications for realistic core-collapse supernova progenitor models will be discussed. I will also present a new method to characterize pre-supernova convection, the method of Vector Spherical Harmonics decomposition, and discuss how it can be used to make realizations of core-collapse models in future simulations.
12/14 Shunsuke Hozumi (Shiga University) Intrisic Properties of the Bars Formed by the Bar Instability in Flat Stellar Disks
Recent observations have revealed that some properties of galactic bars have been uncovered on a statistically meaningful levels of accuracy using a large sample of galaxies. As a result, it has been found that bars in SB0-SBb galaxies are longer than those in SBc to SBd galaxies. Furthermore, also found are such properties that the longer bars have larger amplitudes, and show more elongated shapes. However, these systematic bar properties have never been explained physically. In this talk, I show the properties of the bars formed by the bar instability for flat stellar disk models which are constructed on the basis of exact equilibrium distribution functions. Then, I demonstrate that the properties of the simulated bars are, in large measure, similar to those of the observed bars, and that the amplitude, length, and axis ratio are strongly correlated to an initial typical Toomre's Q value. Taking into consideration these results, I discuss what the Hubble sequence represents.
1/6 Federico García (Argentine Institute of Radio Astronomy) Probing generalized Kerr spacetimes through accretion disks
In General Relativity, black holes are usually described by the Kerr metric. According to Penrose's Cosmic Censorship Conjecture (CCC), curvature singularities are always hidden behind an event horizon. Through this talk, we will explore the effects caused by an external magnetic field on observable properties of accretion disks in Kerr spacetimes with and without horizons. We will use a ray-tracing algorithm to calculate X-ray thermal spectra and relativistic emission-line profiles as well as light curves and power spectra of hot spots on thin accretion disks, considering uniform and dipolar magnetic field configurations, which might be exploited to probe the CCC and to estimate the existence and global geometry of magnetic fields around compact objects in X-ray binaries and/or AGN.
1/19 Alexander Heger (Monash Center for Astrophysics) Nucleosynthesis of the First Stars
The first stars mark the transition from a universe solely composed out of hydrogen and helium to one in which heavier elements - metals -, govern many aspects of the evolution of stars and galaxies. The first stars are very unique due to their pristine primordial initial composition, changing both how these stars form and how they evolve. They have different structures than their metal-rich counterparts and they may die in supernovae in different ways and as different kinds of supernovae than modern stars. All these differences result in a very unique nucleosynthesis output from this first generation of stars, that, however, is sensitive to the various details of each of the stars. The peculiar formation environment of primordial stars gives rise to speculations, supported by theory and numerical simulations, that these stars, on average, were significantly more massive than present-day stars. In this seminar I will first give an overview of the evolution and supernovae of massive stars in general and of Population III stars in particular. I will then discuss their nucleosynthesis signatures as possible diagnostics that can be used to probe their properties using observations of abundance patterns in old halo stars today.
1/25 Fumi Egusa (NAOJ) Spiral Structure in Galactic Disk
In the local universe, more than half of galaxies are categorized as a disk galaxy, which often exhibit a spiral structure. Meanwhile, the fraction of disk galaxies is lower in the distant universe. It it thus likely that the fraction has increased as the universe evolves. However, how disk galaxies and their spiral structure have evolved and reached to the current status is not fully understood yet. In this talk, I will focus on the nature of spiral structures based on observational studies of nearby galaxies. Theoretical models on spiral structure can be divided into two in terms of its lifetime: long-lived (density wave) or short-lived (swing amplification, tidal arms). I will present how these models are compared to observational results.
2/1 Ryo Tazaki (Kyoto University) Multiwavelength polarimetric properties of protoplanetary disks
In order to constrain the grain properties in protoplanetary disks by observations, we studied the origin of polarized light of disks from near-infrared to millimeter wavelengths. First of all, we developed an analytical method to calculate the light scattering properties of fractal dust aggregates, and then we applied it to the radiative transfer calculation of the disk. As a result, we found that the near-infrared wavelength polarimetry is an useful tool to constrain the size and internal structure of dust aggregates. Secondly, we showed that the high degree of polarization observed in the GG Tau circumbinary ring in near-infrared wavelength can be explained by the presence of fluffy dust aggregates. Next, we investigated grain alignment in the disk as a candidate of the polarized emission from mid-infrared to millimeter wavelengths domain. As a result, we showed that grain alignment can occur in the disk in terms of radiative torques, and can be a source of polarized emission in these wavelengths. In addition, alignment axis has been believed as the magnetic field; however, we found that in most cases, alignment axis in the disk is not to be the magnetic field, but the direction of radiative flux.
2/15 Alexey Tolstov (Kavli IPMU) First stars, hypernovae, and superluminous supernovae: simulations of multicolor light curves and spectra
The phenomenon of a supernova in most cases should start with a bright flash caused by a shock wave emerging on the surface of the star. Thus, some features of the physics of radiation-dominated shock are important for correct numerical modelling of supernova light curves. With account of those peculiarities, we construct a number of models for first supernovae, hypernovae, superluminous supernovae (SLSNe) based on multigroup radiation transfer coupled to hydrodynamics. The results of our numerical simulations of light curves and spectra can be used to analyze and interpret available and future data from space and ground-based observatories. The modeling of first supernovae, hypernovae and SLSNe is also one of the way to shed some light on a possible connection of these phenomena.
3/1 Tatsuya Satsuka (Osaka University) Evolution of binary seeds in collapsing protostellar cloud
It is widely recognized that the majority of main-sequence stars and pre-main-sequence stars are in binary systems and that these binaries have various distributions in mass ratio q, binary separation, and binary frequency. The seed binaries are considered to form via fragmentation process. After the fragmentation, the seed binary start to accrete the surrounding envelope and grow towards main-sequence stars. In order to understand the distributions of binaries, we need to investigate the evolution of binaries from seeds to stars. Previous works have studied the gas accretion on to binary assuming constant angular momentum and density of gas at the outer boundary. However, these distributions of gas density and gas angular momentum are unrealistic incollapsing protostellar cloud. We perform 3D smoothed particle hydrodynamics (SPH) simulations of gas accretion on to the seeds of binary stars to investigate their short-term evolution. Taking into account the dynamically evolving envelope with non-uniform distribution of gas density and angular momentum of accreting flow, our initial condition includes a seed binary and a surrounding gas envelope, modelling the phase of core collapse of gas cloud when the fragmentation has already occurred. We run multiple simulations with different values of initial mass ratio q0 (the ratio of secondary over primary mass) and gas temperature. For our simulation setup, we find a critical value of qc = 0.25 which distinguishes the later evolution of mass ratio q as a function of time. If q0 > qc, the secondary seed grows faster and q increases monotonically towards unity. If q0 < qc, on the other hand, the primary seed grows faster and q is lower than q0 at the end of the simulation. Based on our numerical results, we analytically calculate the long-term evolution of the seed binary including the growth of binary by gas accretion. We find that the seed binary with q0 > qc evolves towards an equal-mass binary star and that with q0 < qc evolves to a binary with an extreme value of q. Binary separation is a monotonically increasing function of time for any q0, suggesting that the binary growth by accretion does not lead to the formation of close binaries.
3/8 Benjamin Wu (NAOJ DTA) Star cluster formation triggered by giant molecular cloud collisions
Most stars form in clusters within giant molecular clouds (GMCs). However, the dominant processes that induce the collapse and fragmentation of GMCs into star-forming clumps are poorly understood. One major driver of star formation activity in galactic disks may be triggering via converging molecular flows, i.e., GMC-GMC collisions. Cloud collisions are difficult to observationally verify, but the list of candidates is growing. We carry out 3D, magnetohydrodynamics (MHD), adaptive mesh refinement (AMR) simulations to study how cloud collisions trigger formation of dense filaments, clumps, and star clusters. We include heating and cooling based on photo-dissociation region (PDR) models, supersonic turbulence, magnetic fields, and a new magnetically-regulated star formation model. Comparing and contrasting non-colliding and colliding GMCs, we characterize morphologies of dense gas, magnetic field structure, kinematic signatures of clouds and stars, star cluster properties, and overall star formation rates (SFR). We present key observational diagnostics of cloud collisions and find that typical collisions indeed trigger earlier and enhanced star formation, resulting in 10 times higher SFRs and efficiencies.