10月27日（火）13：30～15：00 太陽系小天体セミナー zoom
Oct 27 Tue Solar System Minor Body Seminar
10月28日（水）13：30～15：00 NAOJ Science Colloquium zoom
Oct 28 Wed
10月28日（水）15：00～16：00 ALMA-J seminar zoom
Oct 28 Wed
10月29日（木）14：00～15：00 Tea Talk zoom
Oct 29 Thu
10月30日（金）13：30～15：00 Solar and Space Plasma Seminar zoom
Oct 30 Fri
詳細は以下をご覧下さい。
10月27日（火）
- キャンパス
- 三鷹
- セミナー名
- 太陽系小天体セミナー
- 定例・臨時の別
- 定例
- 日時
- 10月27日（火曜日）13時30分～15時
- 場所
- zoom
- 講演者
- 大澤亮
- 連絡先
- 名前：渡部潤一
- 備考
- テレビ会議またはスカイプによる参加も可
10月28日（水）
- Campus
- Mitaka
- Seminar
- NAOJ Science Colloquium
- Regularly Scheduled/Sporadic
- Every Wednesday
- Date
- 2020 October 28
- Time
- 13:30-15:00
- Place
- Zoom
- Speaker
- Keiichi Wada (Kagoshima Univ.)
- Title
- Formation of “Blanets” in the Active Galactic Nuclei
- Abstract
- Without doubt, planets are formed from proto-planetary disks around
stars, and more than four thousand exoplanets have been discovered until
now. However, proto-planetary disks may not be the only site of
forming planets in the universe. Recently we proposed a novel site for
“planet” formation, namely circumnuclear gas disks around supermassive
black holes (SMBHs). Most galaxies harbour SMBHs whose masses are
ranged from a few million to billion solar masses. Accretion disks
around SMBHs emit enormous energy owing to mass accretion to the
SMBHs, which are known as the `central engine’ of active galactic
nuclei (AGNs). They are believed to be surrounded by dense, dusty gas,
which obscures the emission from the accretion disks. As a result,
there should be a co\ld dust disk beyond several parsecs from the AGN.
In Wada, Tsukamoto, & Kokubo (2019), we investigated growth history
from sub-micron sized icy monomers to km-sized planetesimals in
circumnuclear disks around SMBHs, based on recent plausible theories
of planetesimal formation around stars. We improved this the model
this year in Paper II, including the effect of the radial drift of the
dust aggregates. We found that “blanets” = black hole planets whose
mass is 100-1000 Earth masses could be formed around some AGNs. - NAOJ Science Colloquium Home page:
- https://sci.nao.ac.jp/seminars/colloquium/
- Facilitator
- -Name：Akimasa Kataoka
10月28日（水）
- Campus
- Mitaka
- Seminar
- ALMA-J seminar
- Regularly Scheduled/Sporadic
- Every Wednesday
- Date and time
- 2020 Oct 28 15:00-16:00
- Place
- Zoom
- Speaker
- Satoshi Ohashi
- Affiliation
- RIKEN
- Title
- Inconsistency and possible solution for grain size measurements of the polarization and spectral index at millimeter wavelengths in protoplanetary disks
- Abstract
-
Recent ALMA polarization observations allow us to look into the dust grain properties in protoplanetary disks (PPDs). One of the main mechanisms of the millimeter-wave polarization has been proposed to be self-scattering. Because the polarization due to the self-scattering becomes most efficient if grain size is comparable to the observing wavelength, the polarization observations have suggested that the typical grain size in PPDs is about 100 micron. On the other hand, there is another method of measuring particle size, the spectral index, which is based on multi-wavelength observation. ALMA and VLA continuum observations have suggested that the grain size needs to be as large as cm.
To understand the inconsistency of the grain size measurements, we have performed the ALMA polarization observation toward three PPDs (HD 142527, HD 163296, and IRS 48). Based on the observations and radiative transfer calculations, we found that the polarization mechanisms are related to the grain size. We propose that the inconsistency can be solved by the dust segregation with coarse spatial resolution (HD 142527 and HD 163296) and/or high optical depth at millimeter wavelengths (HD 142527 and IRS 48). - Facilitator
- Daisuke Iono, Andres Guzman
10月29日（木）
- キャンパス
- 三鷹
- セミナー名
- Tea Talk
- 定例・臨時の別
- 臨時
- 日時
- 10/29（木）14：00～15：00
- 場所
- Zoom
- 講演者
- ランドック・ラムゼイ
- 所属
- 天文情報センター
- タイトル
- ロジックモデルとは何か。どのように活用するか。
- 連絡先
- -名前：藤田登起子
10月30日（金）
- Campus
- Mitaka
- Seminar
- Solar and Space Plasma Seminar
- Regularly Scheduled/Sporadic
- Regular
- Date and time
- 30 October (Fri), 13:30-15:00
- Place
- zoom
- Speaker
- Yohei Kawazura
- Affiliation
- Tohoku University
- Title
- Ion vs. electron heating in astrophysical gyrokinetic turbulence
- Abstract
- Many astrophysical systems, such as solar wind, accretion flows, and interstellar media are collisionless. Therefore, ions and electrons in these systems may have different temperatures. What sets the temperature difference between ions and electrons? This study aims at providing an answer to this question by focusing on plasma heating via the dissipation of turbulence. While kinetic theories are necessary to explore collisionless plasma, it is too difficult to solve kinetic turbulence using Vlasov equation. Thus, we use gyrokinetics (GK), which is a popular model in magnetic confinement fusion studies. In GK, we average out cyclotron motion of particles, which reduces the degree of freedom in phase space to 5D. We computed ion vs. electron heating in Alfvenic and compressive turbulence via hybrid-GK simulations. The results show that ions are preferentially heated over electrons in most of the cases, and electron preferential heating is possible only in low-beta and purely Alfvenic turbulence. In this seminar talk, I will also show our results on electromagnetic spectra in kinetic scale and phase-space cascade.
- Facilitator
- -Name：Munehito Shoda