Colloquium のバックアップ(No.78)

DTA Colloquium 2018 †

DTA Colloquium(理論コロキウム)は原則として毎週火曜日の午後13:30から開催しています。
原則として英語で講演していただきますが、講師・参加者が日本人だけの場合は日本語に切り替えてくださっても（英語のままでも）結構です。
台内・台外また分野を問わず広く発表者（台外の方には旅費・謝金あり）を募集しています。
お問い合わせは以下のコロキウム係までお願いします（_AT_を@に変更してください）。

滝脇知也 takiwaki.tomoya_AT_nao.ac.jp
荻原正博 masahiro.ogihara_AT_nao.ac.jp
楠根貴成 takayoshi.kusune_AT_nao.ac.jp
高橋博之 takahashi_AT_cfca.jp
朝比奈雄太 asahina_AT_cfca.jp
佐々木宏和 hiro.sasaki_AT_nao.ac.jp

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Schedule & History †

FY2010 FY2011 FY2012 FY2013 FY2014 FY2015 FY2016 FY2017

Date	Speaker	Title	Place/Time	Remarks	Organizer
04/05	all internal members	self-introduction	Rinko room, Main Building (East) / 13:30	Thursday	Takiwaki
04/10	Adriana Pohl (Max-Planck Institute of Astronomy, Heidelberg Germany)	Revealing the evolution of planet-forming disks with polarization observations	Lecture room / 13:30	Tuesday	Ogihara
04/17	Yoshiaki Kato (Riken)	Radiation MHD Simulations of Waves and Vortices on the Sun and beyond	Lecture room / 13:30		Takahashi
04/24	Akihiro Suzuki (NAOJ)	Multi-dimensional modeling of supernova ejecta with a central energy source	Rinko room, Main Building (East) / 13:30		Ogihara
05/08	Yoshiyuki Inoue (Riken)	Coronal Magnetic Activity in a Nearby Active Supermassive Black Hole	Rinko room, Main Building (East) / 13:30		Asahina
05/10	Keiichi Maeda(Kyoto University)	Progenitor Evolutions and Explosion Mechanisms of Type Ia Supernovae	Rinko room, Main Building (East) / 15:00	Thursday	Asahina
05/15	Kyohei Kawaguchi (ICRR)	Radiative-transfer simulation for the optical and near-infrared electromagnetic counterparts to GW170817	Lecture room / 13:30		Takahashi
05/22	Kazumi Kashiyama (University of Tokyo)	The repeating fast radio burst and the young neutron star model	Rinko room, Main Building (East) / 13:30		Ogihara
05/29	ShingChi Leung (IPMU)	Pulsation Pair-instability Supernova: Connection to massive black hole, circumstellar medium and collapsar	Lecture room / 13:30		Sasaki
06/05	Doris Arzoumanian (Nagoya University)	Observed properties of nearby molecular filaments	Lecture room / 13:30		Kusune
06/12	Teppei Minoda (Nagoya University)	The effect of the primordial magnetic fields on the cosmic microwave background anisotropy	Lecture room / 13:30		Kusune
06/26	TBA		Rinko room / 13:30
07/03	Shota Notsu (Kyoto University)	Possibility to locate the position of the H2O snowline in protoplanetary disks through spectroscopic observations	Lecture room / 13:30		Ogihara
07/10	Riouhei Nakatani (University of Tokyo)	Radiation Hydrodynamics Simulations of Photoevaporation of Protoplanetary Disks: Metallicity Dependence of UV and X-Ray Photoevaporation	Lecture room / 13:30		Kusune
07/17	TBA		Lecture room / 13:30
07/24	Shunsuke Ideguchi	TBA	Rinko room, Main Building (East) /13:30		Sasaki

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Confirmed speakers †

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Abstract †

4/10 Adriana Pohl (Max-Planck Institute of Astronomy, Heidelberg Germany) Revealing the evolution of planet-forming disks with polarization observations: Recent observational instruments like VLT/SPHERE and ALMA have reached an unprecedented level of resolution and sensitivity. Meanwhile, even the direct observation of substructures in planet-forming disks is within reach, by which the disk evolution can be traced. Features such as gaps, rings, spiral arms and clumps can be either associated with embedded, but yet unseen forming planets, or be related to other internal, physical disk processes. In this talk, I will compare theoretical predictions of dust evolution models and planet-disk interaction processes with current multi-wavelength observations of planet-forming disks. To this end, detailed radiative transfer calculations are presented, which are employed to model observational signatures in disks. An emphasis is placed on polarization diagnostics, which facilitates the detection of light scattered by dust grains in the disk. The latter is a crucial ingredient to constraining the size and composition of dust grains, which is necessary to understand the earliest stages of planet formation.

04/17 Yoshiaki Kato (Riken)　Radiation MHD Simulations of Waves and Vortices on the Sun and beyond: One of the long-standing problems in solar physics is to understand a mechanism which maintains the solar atmosphere. The chromosphere, a layer between the photosphere and the corona, is a key to unveiling the mystery of the solar atmosphere. It is yet to be revealed entirely by observations because the chromosphere has complex structure and rapid variability. Therefore, radiation magnetohydrodynamic (RMHD) simulations play a major role for understanding such a complexity, which is difficult to interpret physical processes. I introduce my recent publications on the effect of MHD waves associated with an isolated magnetic flux concentration (or a flux tube), which is anchored in the photosphere and extended over the corona. This is a classical problem which is extensively discussed in many literatures and probably the best example to understanding MHD waves. While all studies so far relied on inflicting driving forces in the photosphere, only a self-consistent RMHD simulation of the solar atmospheric layers from the surface convection zone to the corona can resolve the realistic nature of MHD waves. First, I present the generation and propagation of mostly slow mode waves, driven by magneto-convective processes in the deep photosphere and beneath it. This is so-called magnetic pumping process which generates slow modes that propagate upward and develop into shock waves in the chromosphere. The magnetic pumping is a robust mechanism for generating shock waves in the vicinity of strong flux tube at the chromospheric height and therefore it’s most likely to sustain the chromosphere. Second, I present the identification of torsional waves in the chromosphere and the corona. Vortical flows in the upper convection zone and the photosphere force magnetic field structures to rotate and thus produce so-called solar “magnetic tornadoes”, which extend into the corona. Unlike slow modes, large portions of torsional modes can reach the corona without suffering significant dissipation and therefore it’s capable of sustaining the corona. Third, I present the detection of physical phenomena in the flux tube by magnetic pumping imprinted on the spectral lines. Thanks to the rapidly advancing solar observations over the past decades, we will have an unique opportunity to grasp the quantitative nature of MHD waves in the near future. It will enable us to extend our knowledge of plasma into those of the other astrophysical objects. Finally, I will briefly talk about the future perspective on my research in the next decades.

04/24 Akihiro Suzuki (NAOJ)　Multi-dimensional modeling of supernova ejecta with a central energy source: Core-collapse supernova explosions are of fundamental importance in the universe. They are an outcome of massive star formation and evolution and at the same time affect their surrounding environments in various ways. This is the reason why many supernova researches and surveys have been intensively conducted. One of the remarkable successes of modern transient survey programs is the discovery of an extremely bright class of core-collapse supernovae, called superluminous supernovae. Because of their high brightness, we can detect high-z events, potentially making it possible to probe star-forming activity even in the high-z universe. However, the problem is that the energy source of their bright emission is still debated. A promising scenario for superluminous supernovae is the central engine scenario, in which the compact remnant (highly rotating neutron star, black hole accretion disk, or whatever) left in the supernova ejecta play a role in giving rise to bright thermal emission. However, there are many remaining problems, such as, how exactly the additional energy deposition is realized and how the supernova ejecta with a central engine evolve. I’m lately investigating the hydrodynamic evolution of supernova ejecta with such a central energy source by using multi-dimensional numerical simulations. In this talk, after a brief introduction of supernovae, I present results of my recent studies.

05/08 Yoshiyuki Inoue (Riken)　Coronal Magnetic Activity in a Nearby Active Supermassive Black Hole: Black hole coronae are believed to be heated by their magnetic activity like the Sun. However, magnetic fields in the vicinity of active supermassive black holes have never been measured. Recently, we proposed a coronal radio synchrotron emission model for Seyfert galaxies. Here, we report the first detection of coronal radio synchrotron emission from a nearby Seyfert galaxy, which enables us to estimate the coronal magnetic field strength. We also found that coronae are composed of thermal and non-thermal electrons. Our results indicate that magnetic activity cannot sustain X-ray emitting coronae. Existence of non-thermal electrons in coronae implies that Seyfert galaxies may explain not only the cosmic X-ray background radiation but also the cosmic MeV gamma-ray background radiation.

05/10 Keiichi Maeda(Kyoto University)　Progenitor Evolutions and Explosion Mechanisms of Type Ia Supernovae: I will provide a review on the current status of observational constraints on the progenitor systems and explosion mechanisms of type Ia Supernovae (SNe Ia). Recent development in the field is highlighted by accumulating observational discoveries of diversities found for SNe Ia. An idea is emerging that SNe Ia are perhaps not at all a uniform system as previously believed for many years, and thermonuclear explosions may lead to various outcomes which could correspond to various types of transients. In this talk, I will summarize different observational constraints placed for different sub-types of SNe Ia and related phenomena, and connect these findings to different types of progenitors and modes of explosions which have been theoretically predicted.

05/15 Kyohei Kawaguchi (ICRR)　Radiative-transfer simulation for the optical and near-infrared electromagnetic counterparts to GW170817: Recent detection of gravitational waves from a binary-neutron star merger (GW170817) and the subsequent observations of electromagnetic counterparts provide a great opportunity to study the physics of compact binary mergers. The optical and near-infrared counterparts to GW170817 are found to be consistent with a kilonova/macronova scenario with red and blue components. However, in most of previous studies in which contribution from each ejecta component to the lightcurves is separately calculated and composited, the red component is too massive as dynamical ejecta and the blue component is too fast as post-merger ejecta. In this talk, I present our recent works performing 2-dimensional radiative-transfer simulations for a kilonova/macronova consistently taking the interplay of multiple ejecta components into account, and show that the lightcurves of optical and near-infrared counterparts can be reproduced naturally by a setup consistent with the prediction of the numerical-relativity simulations.

05/22 Kazumi Kashiyama (University of Tokyo)　The repeating fast radio burst and the young neutron star model: Fast radio bursts (FRBs) are enigmatic radio transients with large dispersion measure. There are ~ 30 of FRBs discovered so far and only one of them, FRB121102, repeats. Recently, the host galaxy and persistent radio counterpart have identified for this repeating FRB. First, I will overview the observational results and the general implications. Then, I will focus on the young neutron star model for FRBs and discuss how one can test the model observationally. In particular, I will discuss the possible connection between FRBs and energetic supernovae.

06/05 Doris Arzoumanian (Nagoya Universiry)　Observed properties of nearby molecular filaments: The highly filamentary structure of the interstellar medium is impressively revealed by the unprecedented quality and sky coverage of Herschel and Planck images tracing the Galactic cold dust emission. These observations provide the required data to describe in detail the properties of the filamentary structures observed in both quiescent clouds and in star forming regions, where the densest filaments appear to be the main sites of star formation. The omnipresence of filaments in observations as well as in numerical simulations suggests that the formation of filamentary structures is a natural product of the interplay between interstellar shock waves, gravity, and magnetic fields. The detailed description of their observed properties is important to improve our understanding of their formation and evolution process. I will present what we have learned about the properties of the filamentary structures derived from Herschel dust continuum and ground based single dish molecular line observations, and I will discuss the observational constraints on the formation and evolution of molecular filaments.

06/12 Teppei Minoda (Nagoya University)　The effect of the primordial magnetic fields on the cosmic microwave background anisotropy: The magnetic fields are ubiquitous on the astronomical objects, from asteroids to clusters of galaxies. The origin of these cosmic magnetic fields is unknown, however, while the magnetogenesis in the early universe (such as inflation, the cosmic phase transition, the perturbation evolution, and so on) might be able to explain it. Magnetic fields generated by such cosmological mechanisms are called the primordial magnetic fields (PMFs), and some papers have pointed that the PMFs induce the matter density fluctuation due to their Lorentz force, and also affect the gas temperature distribution through a magnetic dissipation, so-called “ambipolar diffusion”. We consider these effects and calculate the time evolution of the baryon gas density and temperature before the formation of the first stars and galaxies. And we suggest a method to investigate such primordial gas structure with the cosmic microwave background (CMB) temperature anisotropy. In this talk, I will briefly introduce the PMFs and its general formalism, and review some basic concepts of the standard cosmology and CMB physics. Next, I will talk about the effect of the PMFs on the baryon gas history, and finally show the calculation method and the results of my recent work (Minoda et al., 2017, Phys. Rev. D, 96, 123525).

07/03 Shota Notsu (Kyoto University) Possibility to locate the position of the H2O snowline in protoplanetary disks through spectroscopic observations: Observationally locating the position of the H2O snowline in protoplanetary disks is important for understanding the planetesimal and planet formation processes, and the origin of water on Earth. The velocity profiles of emission lines from disks are usually affected by Doppler shift due to Keplerian rotation. Therefore, the line profiles are sensitive to the radial distribution of the line-emitting regions. In our studies (Notsu et al. 2016, ApJ, 827, 113; 2017, ApJ, 836, 118; 2018, ApJ, 855, 62), we calculated the chemical composition of the disks around a T Tauri star and a Herbig Ae star using chemical kinetics, and then the H2(16)O and H2(18)O line profiles. We found that lines with small Einstein A coefficients and relatively high upper state energies are dominated by emission from the hot midplane region inside the H2O snowline, and therefore through analyzing their profiles the position of the H2O snowline can be located. In addition, we found that H2(18)O lines trace deeper into the disk than H2(16)O lines since the number density of H2(18)O is low (Notsu et al. 2018). Thus these H2(18)O lines are potentially better probes of the position of the H2O snowline at the disk midplane, depending on the dust optical depth. Moreover, H2(18)O and para-H2(16)O lines with relatively lower upper state energies (~a few 100K) can also locate the position of the H2O snowline. There are several candidate water lines that trace the position of the H2O snowline in ALMA Bands 5－10. Finally, we have proposed the water line observations for a Herbig Ae disk HD163296 in ALMA Cycle 3, and partial data were delivered. We constrain the line emitting region (the location of the H2O snowline) and the dust properties from the observations.

07/10 Riouhei Nakatani (University of Tokyo) Radiation Hydrodynamics Simulations of Photoevaporation of Protoplanetary Disks: Metallicity Dependence of UV and X-Ray Photoevaporation: Protoplanetary disks are thought to have lifetimes of several million yr in the solar neighborhood, but recent observations suggest that the disk lifetimes are shorter in a low-metallicity environment. We perform a suite of radiation hydrodynamics simulations of photoevaporating disks with varying the metallicity to study their long-term evolution and the metallicity dependence of mass-loss rates. Our simulations follow hydrodynamics, radiative transfer, and nonequilibrium chemistry in a self-consistent manner. Dust-grain temperatures are also calculated consistently by solving the radiative transfer of the stellar irradiation and grain (re-) emission. In the fiducial case with solar metallicity, including the X-ray effects does not significantly increase the photoevaporation rate when compared to the case with ultra-violet (UV) radiation only. At sub-solar metallicities in the range of Z ≳ 10^{-1.5} Zsun, the photoevaporation rate increases as metallicity decreases owing to the reduced opacity of the disk medium. The result is consistent with the observational trend that disk lifetimes are shorter in low metallicity environments. Contrastingly, the photoevaporation rate decreases at even lower metallicities of Z ≲ 10^{-1.5} Zsun, because dust-gas collisional cooling remains efficient compared to far UV photoelectric heating whose efficiency depends on metallicity. The net cooling in the interior of the disk suppresses the photoevaporation. However, adding X-ray radiation significantly increases the photoevaporation rate, especially at Z ~ 10^{-2} Zsun. Although the X-ray radiation itself does not drive strong photoevaporative flows, X-rays penetrate deep into the neutral region in the disk, increase the ionization degree there, and reduce positive charges of grains. Consequently, the effect of photoelectric heating by far UV radiation is strengthened by the X-rays and enhances the disk photoevaporation.