• 日時：火曜日の16:00～17:00
• 場所：理学部1号館西棟 11階 1109号室(天文学専攻会議室)
• 現在、オンライン（Zoom）で16:15～の開催としています。

  今後の談話会の予定

2020年12月15日(火) 16:15-17:15

Speaker: Takahiro Sudoh 須藤 貴弘 (天文学教室 D3)

2020年12月22日(火) 16:15-17:15

Speaker: Takayuki Tomaru 都丸 隆行 (国立天文台 NAOJ/東大天文)

2021年1月12日(火) 16:15-17:15

Speaker: Masamichi Zaizen 財前 真理 (天文学教室 D2)

  本郷キャンパスでの天文・宇宙物理関係のセミナーアナウンスについて

東大本郷キャンパスの天文・宇宙物理関連のセミナーをアナウンスする際は、
hongo-astrotalks (at-sign) astron.s.u-tokyo.ac.jp
をお使いください。 このアドレスにメールを出すと、以下のグループの構成員に展開されます。

• 天文学教室
• 物理学教室
  • 安東研究室
  • 宇宙理論研究室
  • Ｘ線研究室
  • 山本研究室
• RESCEU

幅広い関係者にメールが展開されることに留意して、多くの人が興味を 持ちそうなセミナー・教室談話会などのアナウンスにお使いください。

  過去の談話会

第1708回 2020年7月14日(火) 16:15-17:15

Title: Development of Monte Carlo Based X-Ray Clumpy Torus Model and Its Applications to Nearby Obscured Active Galactic Nuclei

Speaker: Atsushi Tanimoto 谷本 敦 (Department of Physics, The University of Tokyo)

Language: English

The unification model of an Active Galactic Nucleus (AGN) indicates the ubiquitous presence of dusty clumps (clumpy torus) around the accreting Supermassive Black Hole (SMBH). This torus is a key structure to understand the mechanisms of the coevolution between the SMBH and the host galaxy. This is because the torus is considered as a mass reservoir that feeds mass onto the SMBH from the host galaxy. However, the basic properties of AGN tori (e.g., the spatial distribution of matter and the gas-to-dust ratio) are still unclear. In this talk, we present (1) constructing an X-ray spectral model from a realistic clumpy torus (XClumpy: Tanimoto et al. 2019) and (2) its applications to nearby obscured AGNs (Tanimoto et al. 2020). (1) We constructed the XClumpy model utilizing the Monte Carlo simulation for Astrophysics and Cosmology (MONACO) for the first time. We investigated the dependence of the X-ray continuum and the Fe Ka fluorescence line profile on the torus parameters. (2) We applied the XClumpy model to the broadband X-ray spectra of 10 obscured AGNs. The infrared spectra of these AGNs were analyzed by Ichikawa et al. with the CLUMPY code. Because the XClumpy model adopts the same clump distribution as that in CLUMPY, we can directly compare the torus parameters obtained from the X-ray spectra and those from the infrared spectra. The torus angular widths determined from the infrared spectra are systematically larger than those from the X-ray spectra. The difference correlates with the inclination angle determined from the X-ray spectrum. These results imply that the dusty polar outflows contribute to the observed infrared flux.

(This talk will be given online. Details will be announced via e-mail.)

第1709回 2020年10月13日(火) 16:15-17:15

Title: Enrichment of Heavy Elements in Dwarf Galaxies and the Milky Way

Speaker: Yutaka Hirai 平居 悠 (RIKEN 理化学研究所)

Language: English

Abundances of heavy elements in metal-poor stars help us understand their astrophysical sites and evolutionary histories of galaxies. High-dispersion spectroscopic observations have identified that abundances of neutron-capture elements such as Sr, Ba, and Eu show star-to-star scatters in extremely metal-poor stars in the Milky Way while there is an increasing trend toward lower metallicity in the abundance of Zn. However, their astrophysical sites and the enrichment in galaxies are not well understood. Here I will show the enrichment of heavy elements of dwarf galaxies and the Milky Way using N-body/smoothed particle hydrodynamics simulations. The results suggest that binary neutron star mergers can contribute to the enrichment of Sr, Ba, and Eu for [Fe/H] < −2. Likewise, this study finds that ejecta from supernovae by low-mass progenitors can form stars with high [Zn/Fe] and [Sr/Ba] ratios. In this talk, I will also discuss relationships among abundances of elements, kinematics of stars, and the Milky Way formation.

(This talk will be given online. Details will be announced via e-mail.)

第1710回 2020年10月27日(火) 16:15-17:15

Title: Observing the interplanetary dust grains as meteors

Speaker: Ryo Ohsawa 大澤 亮 (IoA 天文センター)

Language: Japanese (日本語)

Our solar system is filled with plenty of small dust grains, which are generated by small solar system bodies such as comets and asteroids. They are commonly referred to as interplanetary dust. The Earth is orbiting through the interplanetary dust. A number of dust grains are expected to continuously collide with the Earth’s atmosphere. Part of the grain’s kinetic energy is emitted in a form of light or used to ionize the ambient atmosphere, which is recognized as a meteor phenomenon. Measuring the total energy of a meteor brings an estimate of the mass of a single interplanetary dust grain corresponding to the meteor. Meteor observation is a powerful tool to investigate the mass frequency distribution of the interplanetary dust. Faint meteors have been widely observed by radar. A meteor head echo observation is very useful to detect faint meteors caused by small grains, as faint as 10 mag in the visible band. How faint meteors are detected by radar had, however, not been firmly confirmed in any simultaneous observations. This is mainly due to insufficient sensitivity of optical observations. Kiso Observatory, the University of Tokyo, has developed a wide-field mosaic CMOS camera, Tomo-e Gozen, which is able to monitor a wide area of the sky at up to 2 fps. The performance of Tomo-e Gozen enables us to measure the brightness of the same meteors detected by radar. In the presentation, we present the result of simultaneous observations with Tomo-e Gozen and the MU radar carried out in April, 2018. We concluded that 228 meteors were simultaneously detected by radar and in optical. By combining the previous observations, we derive the relationship to convert the radar cross sections into the optical brightness. This illustrates that the meteors detected by the MU radar are as faint as about 9.5 mag in the visible band, corresponding to 10 micrograms in mass. The total mass falling onto the Earth as meteors is estimated to be about 1000 kg/day.

(This talk will be given online. Details will be announced via e-mail.)

第1711回 2020年11月10日(火) 16:15-17:15

Title: Evolution of Low- and Intermediate-mass Stars with Neutrino Magnetic Moment

Speaker: Kanji Mori 森 寛治 (東大天文 D3/国立天文台 NAOJ)

Language: Japanese (日本語)

Observations of the neutrino oscillation have revealed that neutrinos have masses. Particle theories predict that massive neutrinos have magnetic moment, although its value is experimentally unknown. Since the Standard Model of particle physics assumes massless neutrinos, detection of neutrino magnetic moment (NMM) is a key to physics beyond the Standard Model. If NMM is finite, an additional energy loss channel becomes open in stellar plasma and thus stellar evolution is affected. In the first part of this talk, I adopt the effect of NMM on 7—10 M_⊙ stars, which form a loop during central He burning. It is found that the blue loop is eliminated when NMM is adopted. Since a part of stars in the blue loop can be observed as Cepheid variables, the elimination of the blue loop results in the lack of observed Cepheids. In order to avoid the elimination of the blue loop, NMM should be in the range of 2×10^-10μ_B to 4×10^-11μ_B, where μ_B is the Bohr magneton. In the second part, I adopt the effect of NMM on 1 M_⊙ stars. Recently, it is pointed out that observed Li abundances in low-mass red clump stars are significantly larger than model prediction. I found that the additional energy loss induced by NMM helps internal mixing in stars near the tip of the red giant branch and enhance the Li abundance. It is concluded that NMM of (2—5)×10^-12μ_B mitigates the Li problem in low-mass stars.

(This talk will be given online. Details will be announced via e-mail.)