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Colloquium

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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 InstabilityRinkoh room / 13:30
5/24Naonori Sugiyama (IPMU)Kinematic Sunyaev-Zel'dovich effectConference room, Cosmos Lodge / 13:30
5/31Shogo Ishikawa (NAOJ CfCA)The Galaxy-Halo Connection in High-redshift UniverseConference room, Cosmos Lodge / 13:30
6/7Tomoya Kinugawa (U. Tokyo)Compact binary remnants from first stars for the gravitational wave sourceConference room, Cosmos Lodge / 13:30
6/12Yamaç Pehlivan (Mimar Sinan University)Stars as extreme laboratories for neutrino physicsConference room, Cosmos Lodge / 13:30
6/14Cemsinan Deliduman (Mimar Sinan University)Astrophysics with Weyl GravityRinkoh room / 13:30
6/21Hiroyuki Kurokawa (ELSI, Tokyo Tech)Hydrodynamics of first atmospheres of planets embedded in protoplanetary diskConference 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
7/5Yuta Asahina (NAOJ CfCA)MHD Simulations of the Feedback via an AGN outflow to the inhomogenious interstellr mediumConference room, Cosmos Lodge / 13:30
7/12Shoko Oshigami (NAOJ CfCA)Mare volcanism: Reinterpretation based on Kaguya Lunar Radar Sounder dataConference room, Cosmos Lodge / 13:30
7/19Shinsuke Takasao (Nagoya University)MHD Simulations of Accretion onto Star from Surrounding DiskConference room, Cosmos Lodge / 13:30
7/26Jean Coupon (University of Geneva)Probing the galaxy-mass connection in TeraByte-scale imaging surveysConference room, Cosmos Lodge / 13:30
10/11Yuri Aikawa (University of Tokyo)TBDConference 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.
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.
5/24 Naonori Sugiyama (IPMU) Kinematic Sunyaev-Zel'dovich effect
Over the past few years, cosmologists have been able to make the first detections of the kinematic Snuyaev-Zel'dovich (kSZ) effect by combining galaxy data with measurements from CMB experiments. The kSZ effect is well-suited for studying properties of the optical depth of halos hosting galaxies or galaxy clusters. As the measured optical depth via the kSZ effect is insensitive to gas temperature and redshift, the kSZ effect can be used to detect ionized gas that is difficult to observe through its emission, so-called "missing baryons". This work presents the first measurement of the kSZ effect in Fourier space. While the current analysis results in the kSZ signals with only evidence for a detection, the combination of future CMB and spectroscopic galaxy surveys should enable precision measurements. This talk emphasizes the potential scientific return from these future measurements.
5/31 Shogo Ishikawa (NAOJ CfCA) The Galaxy-Halo Connection in High-redshift Universe
We present the results of clustering analyses of Lyman break galaxies (LBGs) at z~3, 4, and 5 using the final data release of the Canada–France–Hawaii Telescope Legacy Survey (CFHTLS). Deep- and wide-field images of the CFHTLS Deep Survey enable us to obtain sufficiently accurate two-point angular correlation functions to apply a halo occupation distribution analysis. The mean halo masses increase with the stellar-mass limit of LBGs. Satellite fractions of dropout galaxies, even at less massive halos, are found to drop sharply, from z=2 down to less than 0.04, at z=3-5, suggesting that satellite galaxies form inefficiently even for less massive satellites. We compute stellar-to-halo mass ratios (SHMRs) assuming a main sequence of galaxies, which is found to provide SHMRs consistent with those derived from a spectral energy distribution fitting method. The observed SHMRs are in good agreement with model predictions based on the abundance-matching method, within 1sigma confidence intervals. We derive observationally, for the first time, the pivot halo mass, which is the halo mass at a peak in the star-formation efficiency, at 3<z<5, and it shows a small increasing trend with cosmic time at z>3. In addition, the pivot halo mass and its normalization are found to be almost unchanged during 0<z<5. Our study provides observational evidence that galaxy formation is ubiquitously most efficient near a halo mass of 10^12Msun over cosmic time.
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.
6/12 Yamaç Pehlivan (Mimar Sinan University) Stars as extreme laboratories for neutrino physics
Neutrinos are the second most abundant particle species in the universe after the photons. Due to their small cross sections, their last point of scattering (and hence their memory) lies deep within dense astrophysical objects. As a new observational window to the Universe, neutrinos hold a great potential. But, an equally exciting possibility is to use these observations as a probe to their minuscule properties under the Universe's most extreme conditions.In this talk, I will focus on the neutrinos emitted by core collapse supernova where, in the deep regions, neutrino-neutrino interactions turn their flavor oscillations into a nonlinear many-body phenomenon. Various tiny neutrino properties can be amplified by these nonlinear effects with detectable consequences. These can show themselves directly in a future galactic supernova signal detected by Super-Kamiokande, or indirectly (through their effect on nucleosynthesis) in elemental abundance surveys by Subaru and TMT.
6/14 Cemsinan Deliduman (Mimar Sinan University) Astrophysics with Weyl Gravity
This talk will introduce an attempt to describe the diverse astrophysical phenomena via Weyl gravity. In the first part I will review my work on the resolution of the flat galactic rotation curve problem via geometry instead of assuming the existence of dark matter. Motivation for this work came from the observation that the scale independence of the rotational velocity in the outer region of galaxies could point out to a possible existence of local scale symmetry and therefore the gravitational phenomena inside such regions should be described by the unique local scale symmetric theory, namely Weyls theory of gravity. Solution to field equations of Weyl gravity will determine the special geometry of the outer region of galaxies. In the second part of the talk it will be conjectured that this special geometry could be valid up to the scale of galaxy clusters. Then one challenge of this approach will be to explain gravitational lens characteristics of galaxy clusters by Weyl geometry without assuming existence of dark matter. Research in this direction will be summarized.
6/21 Hiroyuki Kurokawa (ELSI, Tokyo Tech) Hydrodynamics of first atmospheres of planets embedded in protoplanetary disk
Exoplanet observations revealed that a significant fraction of Sun-like stars harbor super-Earths, here defined as those objects having masses between a few to ~20 Earth masses. Though their masses overlap with the range of core masses believed to trigger runaway accretion of disk gas, these super-Earths retain only small amounts of gas: ~1%-10% by mass. How did super-Earths avoid becoming gas giants? One possible solution is late-stage core formation; super-Earths were formed by the final assembly of proto-cores during disk dispersal (Lee et al. 2014). Another solution is rapid recycling of envelope gas. Ormel et al. (2015) conducted hydrodynamical simulations of isothermal flow past a low-mass planet embedded in disk gas. They found that the atmosphere (inside the Bondi sphere) is an open system where disk gas enters from high latitude (inflow) and leaves through midplane region (outflow). They argued that the recycling is faster than the cooling (namely, the contraction) of the envelope gas, and so that further accretion of disk gas is prevented. To evaluate the influence of the cooling process on the recycling process, we performed non-isothermal hydrodynamical simulations of the flow around an embedded planet, where radiative cooling was approximated by the beta cooling model. We found that the recycling is limited in the non-isothermal cases because of the difference in entropy between the inflow (high entropy) and the atmosphere (low entropy). The high entropy flow cannot penetrate the low-entropy atmosphere, and therefore the recycling is limited to the upper region of the Bondi sphere. Our results suggest that the recycling process may not be able to explain the ubiquity of super-Earths. Nevertheless, the midplane outflow induced by the recycling may prevent or reduce the accretion of pebbles onto proto-cores. This would delay the growth of these cores and help us to explain the ubiquity of super-Earths in the context of the late-stage core-formation scenario.
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.
7/5 Yuta Asahina (NAOJ CfCA) MHD Simulations of the Feedback via an AGN outflow to the inhomogenious interstellr medium
Co-evolution between central supermassive black holes and host galaxies is a hotly debated issue in astrophysics. Outflows are thought to have an impact of the interstellar medium (ISM), and probably be responsible for the establishment of a widely known correlation between black hole mass (M) and the stellar velocity dispersion in galactic bulge (), so-called M- relation. Feedback by the quasar wind has been investigated by Silk & Rees (1998), Fabian (1999), and King (2003). However the quasar winds are assumed to be spherical symmetric outflows. Wagner et al. (2012) studied the feedback via AGN jets. They revealed that the feedback via the AGN jet can be origin of M- relation. Magnetic fields are not included in their simulations, although magnetic fields of 0.01-1 mG have been reported to exist in the galactic center. In order to study the effect of the magnetic field to the feedback via the AGN jet, we carry out 3D MHD simulations. Our simulations reveal that the magnetic tension force promotes the acceleration of the ISM and enhances the feedback efficiency.
7/12 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.
7/26 Jean Coupon (University of Geneva) Probing the galaxy-mass connection in TeraByte-scale imaging surveys
The past decade has seen the emergence of new techniques and exciting discoveries powered by wide-field imaging surveys from the UV to the near-IR domain. Owing to gravitational lensing, galaxy clustering and abundance matching (to name but a few), coupled with advanced statistical interpretation, the informative power of astronomical imaging surveys has significantly increased. In particular, the connection between galaxies and dark matter, a keystone in cosmology and the study of galaxy evolution, has widely gained from this "scale revolution" and the future is bright, as the next experiments such as HSC, LSST, Euclid or WFIRST are dedicated "survey" machines that will further increase imaging data by orders of magnitude (without mentioning the tremendous gain in image resolution, time domain and deep near-IR imaging). I will focus my talk on reviewing the main techniques to connect galaxies and dark matter in the context of wide-field surveys and I will show some concrete examples of applied data analysis in the CFHTLenS and COSMOS projects, showing that these techniques are now well proven, although the challenges in reducing some critical systematic uncertainties are ahead of us.