2020.8.3-2020.8.9

8月3日(月)10:00~12:00 Final Defense for the doctoral thesis of the Department of Astronomical Science, SOKENDAI 
Aug 3 Mon                                     zoom 

8月5日(水)13:30~15:00 NAOJ Science Colloquium         zoom
Aug 5 Wed

8月7日(金)13:30~15:00 Solar and Space Plasma Seminar             zoom
Aug 7 Fri       

詳細は以下をご覧下さい。

8月3日(月)

Campus
Mitaka
Seminar
Final Defense for the doctoral thesis of the Department of Astronomical Science, SOKENDAI
Regularly Scheduled/Sporadic
Sporadic
Date and time
3 August, 10:00~12:00
Place
Mitaka seminar room and zoom
Speaker
Jungha Kim
Affiliation
Department of Astronomical Science, The Graduate University for Advanced Studies, SOKENDAI
Title
Understanding the Circumstellar Structure of High-Mass Young Stellar Objects Based on Interferometric Observations
Facilitator
-Name:Graduate Student Affairs Unit, Research Promotion Group

8月5日(水)

Campus
Mitaka
Seminar
NAOJ Science Colloquium
Regularly Scheduled/Sporadic

Every Wednesday
Date
2020 August 5
Time
13:30-15:00
Place
zoom
Speaker
Yuki Yoshida (Univ. of Tokyo, *Student talk, *Japanese)
Title
Elementary Process of Galactic Spiral Arm Formation: Synchronization of Epicycle Motion by Gravitational Scattering
Abstract
The formation of galactic spiral arms is one of the main problems in the galactic dynamics. Recent studies have shown that spiral arms are transient an d recurrent, an d are considered to be stellar material arms that move as a group. As one of the formation processes, the swing amplification has been considered, in which the leading wave becomes a trailing one by differential rotation an d the surface density is amplified by self-gravity (Julian & Toomre 1966; Toomre 1981). As a mechanism of the swing amplification, the gravitational scattering from density fluctuations in the galactic disk is considered to make a spiral-like structure. Also, N-body simulation of the formation of spiral arms has confirmed that the phase of the stellar orbits is synchronized during the formation of spiral arms (Michikoshi & Kokubo 2016; 2018). Although Julian & Toomre (1966) suggested that there is a relation between the spiral arm formation an d the phase synchronization, no study investigates the relation in detail. We focus on the gravitational scattering by this perturber an d consider the elementary process of swing amplification reduced to the restricted three-body problem. To investigate the orbital evolution an d the phase synchronization of the stellar orbits, we use the epicycle approximation, consider the perturber as a point mass, an d simulate the gravitational scattering by the perturber. We show that the gravitational scattering by the perturber synchronizes the epicycle phase of the stellar orbits. We also investigate the dependence of the phase synchronization on the disk parameter an d the initial stellar orbital elements to identify the conditions of the synchronization. Also, we prepare uniformly distributed groups of stars an d solve the restricted three-body problem of the orbital evolution of each star. We then study the structure of the surface distribution caused by gravitational scattering an d identified the high-density region formed by the swing amplification. The dependence of the structure of the high-density region on the disk parameters an d the initial stellar orbital elements is also studied. From these results, we discuss the conditions of the phase synchronization an d how the condition corresponds to the actual galactic spiral arms.
NAOJ Science Colloquium Home page
URL: https://sci.nao.ac.jp/seminars/colloquium/
Read more
Facilitator
-Name:Akimasa Kataoka

8月7日(金)

Campus
Mitaka
Seminar
Solar and Space Plasma Seminar
Regularly Scheduled/Sporadic
Regular
Date and time
7 August (Fri), 13:30-15:00
Place
zoom
Speaker
Ryouhei Kano
Affiliation
SSO/NAOJ
Title
UV polarimetry to access the solar upper atmosphere
Abstract
There are many spectral lines formed in the upper atmosphere of the
Sun in the ultraviolet (UV) wavelength range, which is an important
window into the physical diagnosis of such upper atmosphere. In
particular, the polarization of some spectral lines has magnetic
information around the layers in which such lines are formed. Recent
studies in the synthetic calculation of polarized spectral line profiles
suggest magnetic sensitivity due to the Hanle effect in the hydrogen
Lyman alpha line (121.6 nm) and magnetic sensitivity due to the Hanle
and Zeeman effects in the Mg II h & k lines (280 nm). By using the core
of these lines, we can access just below the corona (the transition
region or the upper chromosphere), in which the plasma beta is lower
than unity. To establish a magnetic diagnosis in such upper atmosphere,
we have conducted a series of sounding rocket projects, CLASP.
Here, I will present the results of the CLASP series, as well as the
potential of the UV polarimetry in future. I would like to present also
the characteristics of the CLASP instrument as an ultraviolet
instrument, which may provide any hints for future missions like
SOLAR-C_EUVST.
Facilitator
-Name:Munehito Shoda

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