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