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Colloquium のバックアップ(No.63)

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

DateSpeakerTitlePlace/Timeremarksorganizer
04/05all internal membersself-introductionRinko room, Main Building (East) / 13:30ThursdayTakiwaki
04/10Adriana Pohl (Max-Planck Institute of Astronomy, Heidelberg Germany)Revealing the evolution of planet-forming disks with polarization observationsLecture room / 13:30TuesdayOgihara
04/17Yoshiaki Kato (Riken)Radiation MHD Simulations of Waves and Vortices on the Sun and beyondLecture room / 13:30TuesdayTakahashi
04/24Akihiro Suzuki (NAOJ)Multi-dimensional modeling of supernova ejecta with a central energy sourceRinko room, Main Building (East) / 13:30TuesdayOgihara
05/01TBALecture room / 13:30Tuesday
05/08Yoshiyuki Inoue (Riken)Coronal Magnetic Activity in a Nearby Active Supermassive Black HoleRinko room, Main Building (East) / 13:30TuesdayAsahina
05/15Kyohei Kawaguchi (ICRR)TBALecture room / 13:30TuesdayTakahashi
05/22Kazumi Kashiyama (University of Tokyo)TBARinko room, Main Building (East) / 13:30TuesdayOgihara
05/29TBALecture room / 13:30Tuesday
06/05Doris Arzoumanian (Nagoya Universiry)TBALecture room / 13:30TuesdayKusune
06/12Teppei Minoda (Nagoya University)Lecture room / 13:30TuesdayKusune
06/19TBALecture room / 13:30Tuesday
06/26TBALecture room / 13:30Tuesday
07/03TBALecture room / 13:30Tuesday
07/10TBALecture room / 13:30Tuesday
07/17TBALecture room / 13:30Tuesday
07/24TBARinko room, Main Building (East) / 13:30Tuesday
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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.