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Jul 13 Tue 10:00~11:30  太陽系小天体セミナー / Solar System Minor Body Seminar zoom

Jul 14 Wed 15:00 ~16:00 ALMA-J seminar           zoom

Jul 14 Wed 15:30~17:00  NAOJ Science Colloquium      zoom

Jul 15 Thu 14:00~15:00   Tea Talk       zoom

Jul 16 Fri 13:30~15:00   Solar and Space Plasma Seminar   zoom

Jul 16 Fri 16:00~17:00   談話会 / NAOJ Seminar       zoom       






Campus: Mitaka
Seminar: ALMA-J seminar
Regularly Scheduled/Sporadic: Every Wednesday Date and Time: 2021 July 14 15:00-16:00
Place: Zoom
Speaker:Takafumi Tsukui (SOKENDAI/NAOJ)
Title: Rotating gas dynamics and spiral morphology in a galaxy at redshift 4.4
Abstract: Spiral galaxies observed today (redshift z=0) have distinct internal structures: supper massive black hole (SMBH), dense stellar cluster known as bulge; a flat rotating disk; and extended dark matter halo. The cosmic averaged star formation is suggested to peak at z~2. It remains unclear when and how these structures formed and evolved in the cosmic history. Analyzing the rotation curve of rotating gas disk allows us to derive the baryonic (e.g., gas and stars) and dark-matter mass distribution, which is powerful tool to investigate the internal structures of galaxies. We have been establishing a method to derive the mass (distribution) of SMBH, bulge, disk, dark matter halo in nearby galaxies using stellar and gas kinematics. Recently, we investigated publicly available data in the ALMA archive with the motivation of applying the method to further distant galaxies. As a result, we discovered a rotating disk, a central compact structure like a bulge, and spiral structure on the disk in a galaxy at the redshift of 4.4, long before the peak of cosmic star formation. Spiral-arm formation requires disk structure which have been recently discovered by ALMA at similar redshift of z=4 to 5. Although the disk formation epoch is still highly uncertain, our result may indicate that spiral structure has formed in a very short period of time after the disk formation, giving us a new question how the spiral morphology formed in such a short period of time?

Facilitator: Yoshito Shimajiri, Shun Ishii


Seminar:NAOJ Science Colloquium
Regularly Scheduled/Sporadic:Every Wednesday
Date and time:2021 July 14, 15:30-17:00
Speaker:Xingqun Yao
Title:Supernova Nucleosynthesis: Radioactive Nuclear Reactions and Neutrino-Mass Hierarchy
Abstract:We study the sensitivities of nuclear abundances of 7Li, 7Be, 11B, and 11C nuclei to all possible nuclear reactions including short-lived radioactive nuclei in core collapse supernova nucleosynthesis. There is a global trend that the final abundances depend on the variation of n-induced reaction rates for 4+He, 12C and 16O. We also find that p, n, d, t 3He and α particles, which are produced from the n-induced reactions, interact secondarily with primary products 7Li, 7Be, 11B, and 11C, resulting in a remarkable destruction of these nuclei. This mechanism generates nonlinear sensitivity to the primary n-A reaction rates. In particular, the poorly known radioactive nuclear reactions 11C(α, n) are found, for the first time, to affect strongly the final 11C abundance. We discuss the impact on the neutrino oscillation effect which depends on neutrino mass-hierarchy.

Speaker:Kangrou Guo
Title:Planetesimal dynamics in the presence of a giant planet
Abstract:Standard models of planet formation explain how planets form in axisymmetric, unperturbed disks in single star systems. However, it is possible that giant planets could have already formed when other planetary embryos start to grow. We investigate the dynamics of planetesimals under the perturbation of a giant planet in a gaseous disk. Our aim is to understand the effect of the planet’s perturbation on the formation of giant planet cores outside the orbit of the planet. We calculate the orbital evolution of planetesimals ranging from $10^{13}$ to $10^{20}$g, with a Jupiter-mass planet located at 5.2 au. We find orbital alignment of planetesimals distributed in $\simeq 9$-15 au, except for the mean motion resonance (MMR) locations. The degree of alignment increases with increasing distance from the planet and decreasing planetesimal mass. Aligned orbits lead to low encounter velocity and thus faster growth. The typical velocity dispersion for identical-mass planetesimals is on the order of 10 m/s except for the MMR locations. The relative velocity decreases with increasing distance from the planet and decreasing mass ratio of planetesimals. When the eccentricity vectors of planetesimals reach equilibrium under the gas drag and secular perturbation, the relative velocity becomes lower when the masses of two planetesimals are both on the larger end of the mass spectrum. Our results show that with a giant planet embedded in the disk, the growth of another planetary core outside the planet orbit might be accelerated in certain locations. In addition to the results of this paper, I will also show some preliminary results from our follow-up work on the dependence of particle relative velocities on planet parameters (mass and eccentricity).

-Name:Akimasa Kataoka


セミナー名:Tea Talk
講演者:佐藤 幹哉(天文情報センター)
タイトル:ペルセウス座流星群2021 ~8年に1度の好条件~



Campus: Mitaka
Seminar: Solar and Space Plasma Seminar
Regularly Scheduled/Sporadic: Scheduled
Date and time:16 July (Fri), 13:30-15:00
Place: zoom
Speaker:Kazumasa Iwai
Affiliation: Nagoya University
Title:Interplanetary scintillation observation for the solar and heliospheric sciences

Interplanetary scintillation (IPS) is a radio scattering phenomenon caused by the disturbances in the solar wind. The IPS observation using ground-based radio telescopes has been an important technique to investigate the global structure of the heliosphere. ISEE, Nagoya University, have observed the solar wind velocity and density irregularities for several decades using three large radio telescopes at 327 MHz. Because the solar wind connects the Sun and planets including the Earth, the IPS observation can play an important role in both solar physics and space weather. For the space weather point of view, we developed a CME arrival-time forecasting system using a three-dimensional (3D) magnetohydrodynamic (MHD) simulations based on IPS observations. In the developed forecasting system, many MHD simulations with different CME initial speed are tested. The IPS responses of each MHD simulation run is calculated from the density distributions derived from the MHD simulation, and compared with IPS data observed by the ISEE. The CME arrival time of the simulation run that most closely agrees with the IPS data is automatically selected as the forecasted time, which shows the most accurate arrival time. This result suggests that the assimilation of IPS data into MHD simulations can improve the accuracy of CME arrival-time forecasts. We are also developing next generation IPS observation system to investigate the acceleration mechanisms of the solar wind. The current status of the next system and its relationship to the solar missions are summarized in the latter part of the seminar.

-Name:Munehito Shoda
Comment:in English


Campus: Mitaka
Seminar: 談話会 / NAOJ Seminar
Regularly Scheduled/Sporadic: Scheduled
Date and time:16 July (Fri), 16:00-17:00
Place: zoom
Speaker:Stevanus Nugroho
Affiliation: 自然科学研究機構 アストロバイオロジーセンター / NINS Astrobiology Center
Title:Peeking the Atmosphere of Exoplanets using High-resolution Spectroscopy
Using high-resolution spectroscopy, the atomic/molecular bands in the spectrum of an exoplanet are resolved into individual absorption lines. The variation of Doppler shifts caused by the planet’s orbital motion enables absorption lines in the exoplanet spectrum to be distinguished from telluric lines. By combining thousands of unique absorption (or emission) lines, the atomic/molecular signatures can be identified unambiguously and detected at high significance. As it is sensitive to the position of the lines, it also allows us to measure the planetary rotation and wind velocity, as well as search for atmospheric variability and inhomogeneity during the transit. In this talk, I will present our studies in characterising the atmosphere of two ultra-hot Jupiters, WASP-33b which has TiO, Fe I and OH identified in its dayside and KELT-20b which is one of the prime examples of an ultra-hot Jupiter with a potentially variable and inhomogeneous atmosphere.

-Name:青木 和光 / Aoki, Wako

Home > ALMA Jセミナー | Solar and Space Plasma (SSP) Seminar | その他 | 国立天文台談話会 | 太陽系小天体セミナー | 科学研究部コロキウム > 2021.7.12-2021.7.18

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