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Colloquium のバックアップ(No.48)


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も(英語のままでも)結構です。

  • 滝脇知也 takiwaki.tomoya_AT_nao.ac.jp
  • 片岡 章雅 akimasa.kataoka_AT_nao.ac.jp
  • Kenneth Wong ken.wong ATM nao.ac.jp
  • 高橋 博之 takahashi ATM cfca.jp
  • 平居 悠 yutaka.hirai ATM nao.ac.jp

Schedule & History

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

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
9/27Takayoshi Kusune (NAOJ)Magnetic field of the bright-rimmed cloud SFO 74Conference room, Cosmos Lodge / 13:30
10/03Matthew Kenworthy (Leiden Observatory)Looking for exorings towards Beta Pictoris, J1407 and PDS 110Conference room, Cosmos Lodge / 13:30
10/04Yuri Aikawa (University of Tokyo)Deuterium Fractionation in Protoplanetary DisksConference room, Cosmos Lodge / 13:30
10/10Peter Behroozi (University of Arizona)Maximizing Inference from Galaxy ObservationsConference room, Cosmos Lodge / 13:30Tuesday
10/18Ryosuke Hirai (Waseda University)Understanding core-collapse supernovae in binaries with various numerical approachesConference room, Cosmos Lodge / 13:30
10/19Sergey Blinnikov (Institute for Theoretical and Experimental Physics )GRB Central Engines within Superluminous Supernovae and their environmentConference room, Cosmos Lodge / 13:30Thursday
10/25Sho Fujibayashi (Kyoto University)The evolution and mass ejection from the remnant of the binary neutron star mergerConference room, Cosmos Lodge / 13:30
11/01No colloquiumNAOJ decadal workshop
11/02Wanggi Lim (NAOJ)Dust in Infrared Dark CloudsConference room, Cosmos Lodge / 13:30Thursday
11/08No colloquiumDTA workshop 2017
11/15Sanemichi Takahashi (Kogakuin University)Early evolution of protoplanetary disks: a ring-gap structure formationConference room, Cosmos Lodge / 13:30
11/22Wolfgang Loeffler (Heidelberg ARI)Gaia Sky: A 3D visualisation of the Gaia CataloguesConference room, Cosmos Lodge / 13:30
11/29No colloquiumCfCA UM
12/06Kazuyuki Sugimura (Tohoku University)Accretion onto seed BHs: the impacts of anisotropic radiation and gas angular momentumConference room, Cosmos Lodge / 13:30
12/20Yutaka Hirai (NAOJ)The role of enrichment of heavy elements in the chemodynamical evolution of dwarf galaxiesConference room, Cosmos Lodge / 13:30
01/17Kohei Hayashi (NAOJ)The universal dark halo scaling relation for the dwarf spheroidal galaxies in the Local GroupConference room, Cosmos Lodge / 13:30
01/24Hiroshi Kobayashi (NAOJ)Three-Dimensional Radiation-Hydrodynamic Simulation of Clumpy Outflow and Its Application to Supercritical Accretors around Black Holes *practice for the PhD defence. *in JapaneseTBD / 13:30
01/31Misako Tatsuuma (UTokyo)Gravitational Instability of a Dust Layer Composed of Porous Silicate Dust Aggregates in a Protoplanetary Disk *practice for the master thesis defence. *in JapaneseRinko-room/ 13:30
01/31Kanji Mori (UTokyo)Quantum Mechanical Constraint on Carbon Fusion Reaction and Its Impact on Type Ia Supernovae *practice for the master thesis defence. *in JapaneseRinko-room/ 14:15
02/21Kaiki Inoue (Kinki University)TBDRinko-room / 13:30
02/28Takashi Shibata (NAOJ)TBDRinko-room/ 13:30
03/28Tomoyuki Hanawa (Chiba University)TBDLecture-room/ 13:30

Confirmed speakers


4/12 Shing Chi Leung (Kavli IPMU) Nucleosynthesis of Type Ia supernovae
Type Ia supernovae (SNe Ia) are an important class of astrophysical objects. They are the standard candles of the universe and the major sources of iron-peak elements. It is known to be the explosion of a carbon-oxygen white dwarf by thermonuclear runaways. However, many theoretical uncertainties still persist, for example whether the progenitor of SNe Ia belongs to single degenerate or double degenerate scenario. Furthermore, the diversity in observations, such as the subclasses of Type Iax or super-luminous SNe Ia, suggests that the standard picture using the explosion of a Chandrasekhar mass white dwarf is insufficient to explain the variety of the observed SNe Ia. To resolve these, a systematic understanding in SNe Ia nucleosynthesis becomes necessary. In this present, I shall present hydrodynamics and nucleosynthesis results of multi-dimensional models for the explosion phase of SNe Ia. We explore the effects of model parameters on the explosion energetic and its chemical production. The influences of our SNe Ia models to galactic chemical evolution are discussed. I also present constraints on the progenitor properties of some recently observed SNe Ia and their remnants.
4/17 Toshihiko Kawano (LANL/Tokyo Tech) beta-delayed neutron emission and fission for r-process nucleosynthesis
We give a brief summary of our recent development of nuclear reaction theories with a particular focus on nuclear data production for the r-process nucleosynthesis. The topics include calculations of the beta-delayed process for neutron-rich nuclei, where several neutrons can be emitted, and eventually fission may take place as well. Our recent studies on fission itself are also given.
4/19 Masaki Yamaguchi (U. Tokyo) The number of black hole-star binaries discovered by the astrometric satellite, Gaia
Although it is believed that there are 10^8-9 stellar mass black holes (BH) in Milky Way, until now only ~60 BHs have been discovered. Moreover, masses of only a dozen BHs of them are constrained. By discovering more BHs and estimating their masses, we would obtain the mass distribution of BHs with a higher confidence level. This distribution is expected to constrain a theoretical model of the supernova explosion in which a BH is produced as a remnant. Gaia is now operated and have a capability to detect binaries with an unseen companion, such as a BH or a neutron star. Gaia performs a high-precision astrometry with the optical band (0.3-1.0um), and surveys a whole sky, where main observational targets are stars. If a target star has an unseen companion, it should show an elliptical motion on the celestial sphere. Gaia can confirm the companion by detecting such motion. Moreover, this elliptical motion leads to all orbital elements, which enables us to estimate the mass of companion. If this mass is larger than 3 solar masses, we can confirm the companion as a BH. In my talk, I will show how many BHs can be detected by such method with Gaia. Considering the binary evolution, we obtain the number of detectable BHs, ~600, for main sequence targets. This means that Gaia can discover the order of one thousand BHs whose masses can be found, although we know only a dozen such BHs now. We conclude that the astrometric observation for binaries is very powerful method for finding BHs.
4/26 Tomohisa Kawashima (NAOJ) Radiation hydrodynamic simulations of super-critical accretion columns onto neutron stars in ULX-pulsars
Ultraluminous X-ray sources are off-centered, extragalactic X-ray sources with luminosities exceeding the Eddington limit for stellar-mass black holes. After the recent discovery of pulsed X-ray emissions in three ULXs, it is widely thought that some ULXs are powered by super-critical column accretion onto neutron stars. The mechanism of super-critical column accretion is, however, still poorly understood. We have, therefore, carried out two-dimensional radiation hydrodynamic simulations of super-critical accretion columns onto neutron stars, and have found that the super-critical accretion can be realized because the most photons escape from the side wall of accretion columns (i.e., the radiation field is anisotropic in the accretion columns). The simulated accretion columns are luminous enough to be consistent with the observed ULX-pulsars.
5/08 Jonathan C. Tan (University of Florida) Inside-Out Planet Formation
The Kepler-discovered systems with tightly-packed inner planets (STIPs), typically with several planets of Earth to super-Earth masses on well-aligned, sub-AU orbits may host the most common type of planets in the Galaxy. They pose a great challenge for planet formation theories, which fall into two broad classes: (1) formation further out followed by migration; (2) formation in situ from a disk of gas and planetesimals. I review the pros and cons of these classes, before focusing on a new theory of sequential in situ formation from the inside-out via creation of successive gravitationally unstable rings fed from a continuous stream of small (~cm-m size) "pebbles," drifting inward via gas drag. Pebbles first collect at the pressure trap associated with the transition from a magnetorotational instability (MRI)-inactive ("dead zone") region to an inner MRI-active zone. A pebble ring builds up until it either becomes gravitationally unstable to form an Earth to super-Earth-mass planet directly or induces gradual planet formation via core accretion. The planet continues to accrete until it becomes massive enough to isolate itself from the accretion flow via gap opening. The process repeats with a new pebble ring gathering at the new pressure maximum associated with the retreating dead-zone boundary. I discuss the theory’s predictions for planetary masses, relative mass scalings with orbital radius, and minimum orbital separations, and their comparison with observed systems. Finally I speculate about potential causes of diversity of planetary system architectures, i.e. STIPs versus Solar System analogs.
5/10 Shinpei Shibata (Yamagata University) Physics of The Rotation Powered Pulsar
I review physics of the rotation powered pulsars with special interest of how the energy and angular momentum are emitted from the system. I will mention briefly an recent observational result that torque on the neutron stars varies with various time scales. This talk is given in Japanese.
5/17 Tomohiro Ono (Kyoto University) Large-scale Gas Vortex Formed by the Rossby Wave Instability
Large-scale gas vortexes induced by the Rossby wave instability (RWI) are one of the plausible explanations of the lopsided structures recently observed in several protoplanetary disks. For comparison with the observations, it is important to investigate quantitatively the properties of the vortexes formed by the RWI. However, our knowledge on the properties and outcomes of the RWI has been limited until recent years. We have studied the RWI with linear stability analyses and hydrodynamical simulations using the Athena++ code. As a result of the linear stability analyses, we show that the RWI is one of the shear instabilities which are explained by the interaction between two Rossby waves. We also derive the critical condition for the onset of the RWI in semi-analytic form. From the numerical simulations, we investigate the properties of the vortexes formed by the RWI and discuss possible observational predictions. In my talk, I will present our three results on the RWI: (1) the physical mechanism, (2) the critical condition for the onset and (3) the properties of the vortexes.
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 Weyl’s 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 (σ), so-called M-σ 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-σ 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.
9/27 Takayoshi Kusune (NAOJ): Magnetic field of the bright-rimmed cloud SFO 74
Magnetic fields are believed to play an important role in the formation and evolution of molecular cloud. In this talk, I will present the results of near-infrared polarimetric observations toward a bright-rimmed cloud (SFO 74). Bright-rimmed clouds, which are small molecular clouds located at the periphery of the HII regions, are considered to be potential sites for induced star formation by UV radiation from nearby OB stars. The obtained polarization vector maps clearly show that the plane-of-sky (POS) magnetic field structure inside the cloud is quite different from its ambient POS magnetic field direction. By applying the Chandrasekhar-Fermi method, I estimate the POS magnetic field strength toward the two regions inside the cloud. Our results indicate that the magnetic field (configuration and strength) of SFO 74 is affected by the UV-radiation-induced shock. I will discuss the relationship between the POS magnetic field and the cloud structure.
10/03 Matthew Kenworthy (Leiden Observatory) : Looking for exorings towards Beta Pictoris, J1407 and PDS 110
Circumplanetary disks are part of the planet and moon formation process, passing from an optically thick regime of gas and dust through to a planet with retinue of moons and Roche lobe rings formed from the accreted material. There should therefore be a transitional phase where moons are beginning to form and these will clear out lanes in the circumplanetary disk, producing Hill sphere filling 'rings' hundreds of times larger than Saturn's rings. We have seen evidence of these objects transiting their young star - with J1407, and more recently, with the young star PDS 110. This star shows periodic eclipses lasting over two weeks of up to 30% in depth, and the next eclipse is predicted to occur in September this year. The star is 10th magnitude in the belt of Orion, and can be followed in the early morning skies from most places on Earth. We are also following the Hill sphere transit of Beta Pictoris b, a gas giant planet around a nearby bright star, and I will also present the latest light curves from this experiment.
10/04 Yuri Aikawa (University of Tokyo): Deuterium Fractionation in Protoplanetary Disks
Deuterium enrichments in molecules are found in star-forming regions, as well as in Earth’s ocean. Asrtrochemical models show that the enrichment originates in exothermic exchange reactions at low temperatures, which could proceed not only in molecular clouds, but also in the cold regions of protoplanetary disks. In recent years, several groups observed deuterated molecules in disks using ALMA, in order to investigate the significance and spatial distribution of the fractionation. Brightness distributions of deuterated molecular lines vary with species and objects. In TW Hya, DCN is centrally peaked, while DCO+ is offset from the center, which suggests that they are formed via different deuteration paths. In AS 209, on the other hand, DCO+ and DCN emissions show similar distribution. Motivated by these observations, we calculate the reaction network model of deuterium chemistry in protoplanetary disks. Our model includes various deuterated molecules, exchange reactions, and nuclear spin-state chemistry of H2 and H3+, which affects the efficiency of deuterium enrichment. We found that the exchange reaction responsible for the fractionation varies among regions. While the exchange reactions of HD with H3+ and CH3+ are effective, as expected, the exchange reaction of D atom with HCO+ is also found to be important in warm regions and disk surface. As long as cosmic rays penetrate the disk, ortho/para ratio of H2 is found to be almost thermal, which lowers the efficiency of fractionation via CH2D+ compared with previous models which assume that H2 is all in para state. We also discuss the effects of grain size and turbulent mixing on deuterium chemistry.
10/10 Peter Behroozi (University of Arizona): Maximizing Inference from Galaxy Observations
I discuss new methods to combine multiple datasets to maximally constrain galaxy evolution and the galaxy―dark matter halo connection, and show how these methods have already changed our understanding of galaxy formation physics (including why galaxies stop forming stars). Basic extensions to the same techniques allow constraining internal galaxy processes, including coevolution between galaxies and supermassive black holes as well as time delays for supernova / GRB progenitors. Finally, I discuss how these methods will benefit from the enormous amount of upcoming data in widefield (HETDEX, LSST, Euclid, WFIRST) and targeted (JWST, GMT) observations, as well as ways they can benefit observers, including making predictions for future telescopes (especially JWST) and testing which of many possible targeted observations would best constrain galaxy formation physics.
10/18 Ryosuke Hirai (Waseda University ): Understanding core-collapse supernovae in binaries with various numerical approaches
Compact binaries have rapidly attracted attention since the recent detection of gravitational waves from a binary black hole merger event. The two components should have originated from massive stars which experience core-collapse at the end of their lives. However, the evolution of massive stars are extremely uncertain and the presence of a close-by companion complicates it even more. A close binary can undergo mass transfer by overflowing its Roche lobe, or dynamical evolution called common envelope phases when a star plunges into the envelope of the other. Another possible effect is the direct impact of supernova ejecta colliding with its companion when one of the star explodes. In this talk I will discuss the consequence of the "ejecta-companion interaction", using hydrodynamical simulations and stellar evolution calculations. Our results have coincidentally helped us understand the nature of the progenitor system of a supernova called iPTF13bvn. I will also discuss the overall evolution of this progenitor system. If I have time, I will also introduce some of my latest works on numerical techniques.
10/19 Sergey Blinnikov (Institute for Theoretical and Experimental Physics ): GRB Central Engines within Superluminous Supernovae and their environment
Large amounts of mass may be expelled by a star a few years before a supernova explosion. The collisions of SN-ejecta and the dense CSM may provide the required power of light to make the supernova much more luminous. This class of models is referred to as "interacting SNe”. Many SLSNe-I have photospheric velocity of order 10⁴ km/s which is hard to explain in interacting scenario with modest energy of explosion. A strong "hypernova" explosion improves the situation and the properties of SLSNe near maximum light are explained by a GRB-like central engine, embedded in a dense envelope and shells ejected prior the final collapse/explosion of a massive star. In this case velocity up to 1.5x10⁴ km/s is no problem. The problem remains with the nature of the central engine and evolution scenarios leading to double explosions. In view of new LIGO/VIRGO detections of gravitational waves and accompanying events, a few comments and historical remarks will be given.
10/25 Sho Fujibayashi (Kyoto University ): The evolution and mass ejection from the remnant of the binary neutron star merger
We perform general relativistic, long-term, axisymmetric neutrino radiation hydrodynamics simulations for a remnant massive neutron star (MNS) surrounded by a torus, which is a canonical remnant formed after the binary neutron star merger. In this work, we take into account effects of viscosity which is likely to arise in the merger remnant due to magnetohydrodynamical turbulence. We find that two viscous effects play a key role for the evolution of the remnant system and resulting mass ejection. In the first ~10 ms, the structure of the MNS is changed due to the viscous angular momentum transport. As a result, a sound wave, which subsequently becomes a shock wave, is formed in the vicinity of the MNS and the shock wave leads to significant mass ejection. For the longer-term evolution with ~ 0.1--10 s, viscous effects on the torus surrounding the MNS play an important role for mass ejection. The mass ejection rate depends on the viscous parameter for both mass ejection mechanisms, but even for the conservative alpha viscous parameter $\alpha_{\rm vis}\sim0.01$, total ejecta mass is $\sim 5\times 10^{-3}\ M_\odot$ and for $\alpha_{\rm vis}\sim0.04$, it could be $0.02\ M_\odot$. In this talk, I will explain the viscosity-driven mass ejection processes and discuss the electromagnetic signal from the ejecta.
11/02 Wanggi Lim (NAOJ): Dust in Infrared Dark Clouds
The dust grains play key roles to determine physical properties of dense molecular structures. Despite of their importance, our knowledge toward dust properties is mostly dependent on experimental tests and theoretical models due to observational limits on high extinction regions. Here we introduce Mid, Far and Spectroscopic infrared extinction (MIREX, FIREX & SIREX) mapping methods that show the first observational evidence of grain growth in extremely high density regions, i.e. Infrared Dark Clouds. We utilize archival image data of Spitzer-IRAC band 1-4 (3.5 - 8μm), WISE band 3 (12μm), Spitzer-MIPS (24μm) and Herschel-PACS (70μm) in order to make MIREX & FIREX maps of an IRDC, G028.07+00.07. Spectroscopic data of Spitzer-IRS Long-Low slit (15 to 38μm) is analyzed to produce a SIREX map of same IRDC. The pixel by pixel relative extinction laws of the IRDC show the tentative evidence of dust grain growth via coagulation and ice mantle formation in the region of Av~10-100mag. We then compare mass surface density probability distribution functions (Σ-PDFs) of the IRDC and surrounding giant molecular cloud (GMC) that are derived from MIREX map (8μm) and sub-mm (Herschel 160-500μm) dust emission based Σ map (via grey-body fit). The PDFs can be well fit by a single log-normal distribution, with only a small mass fraction (0.03-0.08) in a high Σ power-law tail, even though gas kinematics indicate the IRDC and GMC are self-gravitating with virial parameter α~1. We also show the effect of spectral index β variation against the mass fraction of high-Σ power-law tails.
11/15 Sanemichi Takahashi (Kogakuin University): Early evolution of protoplanetary disks: a ring-gap structure formation
Planets are formed in protoplanetary disks, which are formed around protostars simultaneously with them. Investigation of the early stages of evolution of the protoplanetary disks is important to understand how the star formation and the planet formation processes are connected. Recent observations with ALMA reveal the detailed structures of the protoplanetary disk at the early evolutionary stage. Sheehan and Eisner 2017 found that the gap structure is formed in the protoplanetary disk the protostar WL 17 within about 10 au. Such a structure is thought to be the feature of the old disks (>10^6 yr) called by transition disks. However, the age of WL 17 is estimated to be a few times 10^5 yr. The mechanisms of the gap formation in such young disks have not been investigated well. Sheehan and Eisner 2017 mentioned that the gap structure is formed by the planet. However, the planets forming the gap have not been observed, and it seems difficult to form the planet in the young protoplanetary disks. Thus, it is important to investigate another mechanism for the gap formation in the young disk. In this talk, we discuss the gap formation by the disk wind in the young disks like WL 17 using 1D disk model for the formation and evolution of protoplanetary disks.
11/22 Wolfgang Loeffler (Heidelberg ARI): Gaia Sky: A 3D visualisation of the Gaia Catalogues
The aim of the ESA Gaia mission is to chart the three-dimensional positions and motions of about 1 billion stars in our Milky Way. Gaia Sky is an open-source, multi-platform, real-time, 3D, astronomy software being developed in the Gaia group of the Astronomisches Rechen-Institut (ZAH, Universität Heidelberg) to visualise these positions and motions. We will give an overview of the software features and catalogues which have already been released for the Gaia Data Release 1 and which are under current development for the Gaia Data Relase 2. After briefly touching some technical aspects of the Gaia Sky implementation, we will present some educational and scientific use cases.
12/06 Kazuyuki Sugimura (Tohoku University): Accretion onto seed BHs: the impacts of anisotropic radiation and gas angular momentum
Seed black hole (BH) growth by gas accretion is supposed to play a crucial role in the formation of supermassive BHs. In this talk, I will present the results of our simulations of accretion onto seed BHs under radiation feedback and explain the impact of anisotropic radiation and gas angular momentum on the accretion flow. Then, I will shortly discuss the growth of Pop III remnant BHs based on our findings.
12/20 Yutaka Hirai (NAOJ): The role of enrichment of heavy elements in the chemodynamical evolution of dwarf galaxies
Recent astronomical observations have shown that there are large star-to-star scatters in the abundances of r-process elements and increasing trend of Zn in extremely metal-poor stars. However, it is not yet clear how the early chemo-dynamical evolution of the building blocks of the Milky Way halo affect the abundances of heavy elements. In this talk, we show that high-resolution N-body/smoothed particle hydrodynamics simulations of dwarf galaxies. We find that galaxies with star formation rates less than 0.001 Msun per year reproduce the observed abundances of r-process elements. On the other hand, r-process elements appear at a higher metallicity in galaxies with star formation rates greater than 0.01 Msun per year. We also find that the ejecta from electron-capture supernovae contribute to stars with [Zn/Fe] > 0.5. The scatters of heavy elements mainly come from the inhomogeneity of the metals in the interstellar medium. We find that timescale of metal mixing is less than 40 Myr. This timescale is lower than that of typical dynamical times of dwarf galaxies. Our results demonstrate that the future observations of r-process elements in extremely metal-poor stars will be able to constrain the early chemo-dynamical evolution of the Local Group galaxies.
1/17 Kohei Hayashi (NAOJ): The universal dark halo scaling relation for the dwarf spheroidal galaxies in the Local Group
Dwarf spheroidal galaxies (dSphs) are are excellent laboratories to shed light on fundamental properties of dark matter because these galaxies are the most dark matter dominated systems. In this talk, we propose the universal dark halo scaling relation for the dSphs in the Milky Way and M31. We calculate the dark halo surface density within a radius, r_max, giving the maximum circular velocity, V_max, with respect to observed dSphs and simulated subhalos associated with MW-sized dark halos, and find that the values of surface densities from pure dark matter simulations are in good agreement with those from observations even without employing any fitting procedures. This implies that this surface density would not be largely affected by any baryonic feedbacks and thus universal. Moreover, all subhalos on the small scales of dwarf satellites are expected to obey the universal relation, irrespective of differences in their orbital evolutions, host halo properties, and observed redshifts. In order to understand the origin of this universal dark halo relation. we also investigate orbital and dynamical evolutions of subhalos and find that most of subhalos evolve generally along the specific r_max - V_max sequence even though these subhalos have undergone different histories of mass assembly and tidal stripping. This sequence, therefore, should be the key feature to understand the nature of the universal scaling relation.
1/24 Hiroshi Kobayashi (NAOJ): Three-Dimensional Radiation-Hydrodynamic Simulation of Clumpy Outflow and Its Application to Supercritical Accretors around Black Holes
We study clumpy outflows from supercritical accretion flow around a stellar mass black hole by means of global three-dimensional (3-D) radiation-hydrodynamic (RHD) simulations. In this work, we find that the radiatively driven outflow with the outflow rate of ~10 LEdd/c2 fragments into many clumps above the photosphere located at a few hundreds of Schwarzschild radius (rS) from the central black hole. Such clumps have a shape of a torn sheet, and are rotating around the central black hole with a sub-Keplerian velocity. The typical clump size is 30 rS or less in the radial direction and is more elongated in the angular directions, ~ hundreds of rS at most. When such clumps pass across the line of the sight of a distant observer, stochastic luminosity variations will be produced. The variation timescales are several seconds for a stellar-mass black hole with mass of ten to several tens of the solar mass and are in rough agreement with the observational results of some ultraluminous X-ray sources (ULXs). Our results thus provide a strong support of a hypothesis that the ULXs are powered by the supercritical accretion onto the stellar mass black hole.
1/31 Misako Tatsuuma (UTokyo): Gravitational Instability of a Dust Layer Composed of Porous Silicate Dust Aggregates in a Protoplanetary Disk
Planetesimal formation is one of the most important unsolved problems in planet formation theory. In particular, rocky planetesimal formation is difficult because silicate dust grains are easily disrupted when they collide. Recently, it has been proposed that they can grow as porous aggregates when their monomer radius is smaller than ~ 10 nm, which can also avoid the radial drift toward the central star. However, the stability of a layer composed of such porous silicate dust aggregates has not been investigated. Therefore, we investigate the gravitational instability of this dust layer. To evaluate the disk stability, we calculate Toomre's stability parameter Q, for which we need to evaluate the equilibrium random velocity of dust aggregates. We calculate the equilibrium random velocity considering gravitational scattering and collisions between dust aggregates, drag by mean flow of gas, stirring by gas turbulence, and gravitational scattering by gas density fluctuation due to turbulence. We derive the condition of the gravitational instability using the disk mass, dust-to-gas ratio, turbulent strength, orbital radius, and dust monomer radius. We find that, for the minimum mass solar nebula model at 1 au, the dust layer becomes gravitationally unstable when the turbulent strength alpha<10^{-5}. If the dust-to-gas ratio is increased twice, the gravitational instability occurs for alpha<10^{-4}. We also find that the dust layer is more unstable in disks with larger mass, higher dust-to-gas ratio, and weaker turbulent strength, at larger orbital radius, and with a larger monomer radius.
1/31 Kanji Mori (UTokyo): Quantum Mechanical Constraint on Carbon Fusion Reaction and Its Impact on Type Ia Supernovae
Type Ia supernovae (SNe Ia) are thought to be thermonuclear explosion of white dwarfs (WDs). Their progenitors are not well understood, but one of popular scenarios is the double degenerate (DD) scenario, which attributes SNe Ia to WD-WD binary mergers. The fate of the WD mergers depends on the rate of 12C+12C reaction. We assume a low energy resonance and impose an upperlimit to the resonance strength using the Wigner limit. The resultant resonant rate is applied to the DD scenario. We show that the strongest possible resonance will enhance the reaction rate by ~10^3 times compared with the standard rate, although some of resonances introduced in previous works are too strong. The resonant rate decreases the ignition temperature of carbon burning, therefore accretion induced collapse occurs more easily and the contribution of the DD scenario to the SNe Ia rate becomes smaller.