国立天文台　セミナー情報　/　Seminar Information

March 18 Mon 15:00-16:30
Solar and Space Plasma Seminar
hybrid; Insei Seminar Room in Subaru Building and Zoom

March 19 Tue 10:00-11:30
太陽系小天体セミナー
Zoom

March 22 Fri 16:00-17:00
NAOJ Seminar
hybrid; Large Seminar Room in Subaru Building and Zoom

詳細は下記からご覧ください。

=============== March 18 Mon===============

Campus： Mitaka
Seminar： Solar and Space Plasma Seminar
Regularly Scheduled/Sporadic： Sporadic
Date and time：18 March (Mon), 15:00-16:30
Place： Insei Seminar Room and Zoom

Speaker：Mr. Takero Yoshihisa
Affiliation：Kyoto University (M2)
Title： One-dimensaional MHD simulation for prominence formation triggered by single heating event

Abstract：

I will review on the thermal non-equilibrium phenomena in the solar atmosphere, and present on my master thesis.
Plasma condensation phenomena in the corona, such as prominences and coronal rain, have been observed for many years. It is not clear whether current models can explain their formation process. In one of the proposed models that explain observational properties, the “evaporation condensation” model, a steady or quasi-steady heating at footpoints of a loop drives dense plasma evaporation into the corona and triggers the condensation.
However, it is natural to think of such steady or quasi-steady heating as the superposition of multiple heating events occurring between multiple magnetic field lines. When studying physical processes along a single magnetic field line, a single heating event should be considered as the basic unit.
We therefore investigate whether condensation occurs when the non-steady single heating event occurs at footpoints of a coronal loop. For this purpose, we set a dipped loop and solve 1.5-dimensional (one-dimensional three-vector components) magnetohydrodynamic equations, including radiative cooling, thermal conduction, gravity, and phenomenological turbulence heating. After reproducing the corona by energy input from imposed velocity perturbation at the footpoints, prominence formation is investigated by adding artificial transient localized heating. It is found that required amount of the heating per unit of time is ∼ 10^3 times larger than in steady cases. The amount of energy reaches nanoflare class. We also perform a parameter survey varying the magnitude of the localized heating rate to investigate the conditions for condensation by transient localized heating. The results show that with sufficiently strong heating, sufficient plasma is supplied to the corona to allow cooling to proceed and condensation to occur. It is essential that the loop temperature decreases and thermal conduction becomes inefficient with respect to cooling. Using the loop length L and the Field length λF, the condition for condensation is expressed as λF ≲L/2 under conditions where cooling exceeds heating.

Facilitator
-Name：Akiko Tei

Comment：Japanese (Slides will be in English)

=============== March 19 Tue===============

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：3月19日（火曜日）10時00分～11時30分
場所：zoom
講演者：大坪貴文

世話人の連絡先
　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

=============== March 22 Fri==============

Campus：Mitaka
Seminar：NAOJ Seminar
Regularly Scheduled/Sporadic：Regular
Date and time：March 22, 2024 16:00-17:00
Place：Zoom/Large Seminar Room (hybrid)

Speaker：Director General, Dr. Saku Tsuneta
Affiliation：National Astronomical Observatory of Japan

Title：素晴らしく面白かった太陽の研究
＝40年の研究生活を振り返って＝

Abstract: これまで約40年近く、大学院生や仲間の研究者の方々と、「ひのとり」の硬Ｘ線望遠鏡、「ようこう」の軟Ｘ線望遠鏡、「ひので」の可視光望遠鏡といった飛び道具に載せる望遠鏡の開発を行ってきました。翔体実験装置の開発をするには、教科書を読むだけでは不十分で、観測装置の構想から設計、製作、試験、打上げ前不具合の徹底追及、そして打上げ、飛翔結果を解析して初めて一人前になれます。衛星実験では規模が大きく開発期間も長いため、この過程を経験することが難しく、衛星実験の合間にロケット実験や気球実験も行ってきました。
談話会では、プロジェクトの立ち上げ方や進め方について自分の経験をもとに論じるのと同時に、国立天文台での6年間について所感を述べたいと思います。

Facilitator
-Name：Fumitaka Nakamura

February 28 Wed 10:30-12:00
Solar and Space Plasma Seminar
hybrid; Insei Seminar Room in Subaru Building and Zoom

February 28 Wed 15:30-16:30
NAOJ Science Colloquium
hybrid; Lecture room and Zoom

詳細は下記からご覧ください。

=============== February 28 Wed ===============

Campus： Mitaka
Seminar： Solar and Space Plasma Seminar
Regularly Scheduled/Sporadic： Sporadic
Date and time：28 February (Wed), 10:30-12:00
Place： Insei Seminar Room and Zoom

Speaker：Dr. Yusuke Kawabata
Affiliation：The National Solar Observatory
Title：Multiline Stokes Synthesis of Ellerman Bombs: Obtaining Seamless Information from Photosphere to Chromosphere

Abstract：
There are many kinds of explosive phenomena caused by magnetic reconnections in the solar atmosphere. Ellerman bombs (EBs) are magnetic reconnection events occurring in weakly ionized and moderate plasma β (~1) environments in the solar photosphere and chromosphere. Owing to the observability of the physical quantities around the reconnection site, EBs are one of interesting observation targets for studying magnetic reconnections. While measuring the magnetic field in the solar corona is still difficult, inferring magnetic field in the chromosphere with high spatial resolution and reasonable temporal cadence will be achieved soon.

One such opportunity is SUNRISE III, which is an international balloon-borne solar observatory employing a 1 m diameter telescope. SUNRISE III will achieve five days of stable observations in a seeing-less environment at altitudes around 37 km. We are developing the Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) as a focal plane instrument for SUNRISE III. SCIP will perform multi-line spectropolarimetric observations, enabling us to seamlessly diagnose the physical quantities (magnetic field, velocity field, and temperature) from the photosphere to the chromosphere.

In this talk, I would like to introduce the capability of SCIP for performing observations of magnetic reconnection events. In addition, I will present our recent study: we used a realistic magnetohydrodynamic (MHD) simulation of EB to study how SCIP will have access to the physical phenomena. We synthesized the polarimetric signals by solving radiative transfer equation based on the physical quantities in the MHD simulation and compared the polarimetric signals with the physical quantities in the MHD results. We found that the multiline observations of SCIP can detect the bidirectional flow associated with the EBs and suggest the height of the reconnection site.

Facilitator
-Name：Akiko Tei

Comment：English

=============== February 28 Wed===============

Campus: Mitaka
Seminar: NAOJ Science Colloquium
Date and time: 2023 Feb. 28 (Wed.), 15:30-16:30
Place: the lecture room / Zoom (hybrid)

Speaker: Kuria Watanabe
Affiliation: SOKENDAI (M2)
Title: The Chemical enrichment and origin of Nitrogen-Rich Galaxies at High Redshift
Abstract:
Chemical properties of young galaxies are important to understand the chemical evolution in galaxy formation. We investigate the origin of abundance ratios in JWST star-forming galaxies (z ~ 4-10) by comparing chemical evolution models.
The high N/O ratio in GN-z11, CEERS_01019, and GLASS_150008 observed with JWST cannot be explained by typical chemical evolution models including AGB stars. We focus on the three candidates of rich nitrogen, the Wolf-Rayet stars (WR), supermassive stars (SMS), and tidal disruption events (TDE). We develop the chemical evolution models of three candidates. Although the Ar/O values of the high N/O galaxies are not obtained, we find that the Ar/O values are the key to distinguishing between the three models. The three models can show the high N/O values as much as the N/O values in GN-z11, CEERS_01019, and GLASS_150008.
Because the time scale of high N/O is very short due to the CCSNe, the massive stars (>25 Msun) should directly collapse into black holes.

Speaker: Yuki Kambara
Affiliation: The University of Tokyo (M2)
Title: Planetesimal accretion in planetesimal rings
Abstract:
In the standard planet formation scenario, planetesimals have been assumed to be smoothly distributed in the radial direction except for the snowline. Recently, however, simulations of gas and dust evolution have shown that planetesimals form only in radially limited locations, such as gas pressure bumps and snowlines, and are concentrated in ring-like regions.
The evolution process of planetesimals distributed in a ring is crucial to understanding planet formation theory. However, the evolution of planetesimal rings has not been studied in detail. In this work, we investigate the evolution of planetesimal rings using N-body simulations. We systematically change the initial width and the total mass of planetesimal rings and investigate the dependence of protoplanet properties on the initial conditions. In all simulations, protoplanets undergo oligarchic growth while ring width expands due to scattering by protoplanets. In planetesimal rings, massive protoplanets tend to be formed around the ring center, while protoplanets far from the center of rings are less massive. Scaled orbital separation depends neither on the initial ring width nor the total mass and is consistent with the estimate in the oligarchic growth model. The width of the expanded planetesimal ring does not depend on the initial ring width but on the total ring mass. The maximum mass of protoplanets depends strongly on the total ring mass and weakly on the initial ring width.

Facilitator
-Name: Kazumasa Ohno

Comment: English