カテゴリー: 国立天文台談話会

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Feb. 27　Mon　　　15:30-17:00 　　　　Solar and Space Plasma Seminar　　Zoom

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Feb. 28　Tue　　　 10:00-11:30　 　　　太陽系小天体セミナー　　　　　Zoom

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Feb. 28　Tue　　　16:00-17:00　 　　　NAOJ Seminar 　　　　 Zoom/Lecture Room(hybrid)

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Mar. 1　 Wed　　 　14:30-15:30 　　　　ALMA-J Seminar 　　 Zoom/ALMA building #102 (hybrid)

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Mar. 1 　Wed　 　　15:30-17:00　　　 　NAOJ Science Colloquium 　　Zoom / Instrument Development Bldg. 3 (hybrid)

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詳細は下記からご覧ください。

=============== Feb 27 Mon ===============

Campus： Mitaka
Seminar： Solar and Space Plasma Seminar
Regularly Scheduled/Sporadic： Scheduled
Date and time：2月27日 (月), 15:30-17:00
Place： Zoom
Speaker：永岡賢一
Affiliation：核融合科学研究所
Title：シアがある系の乱流輸送実験研究ートーラスプラズマと電気対流乱流からの話題提供－
Abstract：乱流輸送は自然界に普遍的にみられる現象であるが、その統計的性質は複雑を極め、いくつかの例外を除いて普遍的性質を見いだせていない。磁場閉じ込め核融合プラズマを目指す研究では、乱流中にゾーナルフローと呼ばれるメソスケール構造が自発的に形成され、乱流輸送を大きく制限し、系のダイナミクスにも影響することがわかってきた。最近、我々はこの非線形過程に支配されるゾーナルフローを外部から制御することに挑戦し、磁場の測地曲率により乱流輸送を制御できることを示した。この実験について紹介し、乱流とシアの関係について、議論する。もう一つは、電気対流乱流を用いた実験では、平行平板間を流れる液晶の乱流実験を紹介する。流れを駆動することは、エネルギー注入スケールのシアを系に導入することになるため、その影響を調べることができる。シアによる乱対流の非対称化と乱流による乱流の等方化の競合状態で、双山の速度分布関数のが見つかった。現象論的なモデルにより、乱流、対流、シアの競合状態の結果として、双山の速度分布関数を再現できた。速度分布関数の計測から系の競合状態の診断可能性を指摘した。時間が許せば、対流不安定、対流安定境界に観測される特徴的な輸送現象についても紹介する。

Facilitator
-Name：Takayoshi oba

-Comment：in English

=============== Feb 28 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：2月28日（火曜日）10時00分～11時30分
場所：zoom
講演者：春日敏測

タイトル：2017年 京都火球と潜在的に危険な地球接近二重小惑星 2003 YT1
Abstract：We present a fireball detected in the night sky over Kyoto,
Japan on UT 2017 April 28 at 15h 58m 19s by the SonotaCo Network. The
absolute visual magnitude is Mv=−4.10±0.42mag. Luminous light curves
obtain a meteoroid mass m=29±1g, corresponding to the size
a_s=2.7±0.1cm. Orbital similarity assessed by D-criterions (cf.
D_SH=0.0079) has identified a likely parent, the binary near-Earth
asteroid (164121) 2003 YT1. The suggested binary formation process is
a YORP-driven rotational disintegration. The asynchronous state
indicates the age of < 1e4yr, near or shorter than the upper limit to
meteoroid stream lifetime. We examine potential dust production
mechanisms for the asteroid, including rotational instability,
resurfacing, impact, photoionization, radiation pressure sweeping,
thermal fracture and sublimation of ice. We find some of them capable of
producing the meteoroid-scale particles. Rotational instability is
presumed to cause mass shedding, in consideration of the recent
precedents, possibly releasing mm-cm scale dust particles. Impacts by
micrometeorites with size≃1mm could be a trigger for ejecting the
cm-sized particles. Radiation pressure can sweep out the mm-sized dust
particles, while not sufficient for the cm-sized. For the other
mechanisms, unprovable or unidentified. The feasibility in the parental
aspect of 2003 YT1 is somewhat reconciled with the fireball observation,
yielding an insight into how we approach potentially hazardous objects.

Kasuga, Sato, Ueda, Fujiwara, Tsuchiya and Watanabe (2020), AJ, 159, 47
https://iopscience.iop.org/article/10.3847/1538-3881/ab4e1b
https://www.nao.ac.jp/news/science/2020/20200115-prc.html

世話人の連絡先
　名前：渡部潤一

=============== Feb 28 Tue ===============

Campus：Mitaka
Seminar：NAOJ Seminar
Regularly Scheduled/Sporadic：Sporadic
Date and time：2023 February 28, 16:00-17:00
Place： Zoom/Lecture Room(hybrid)
Speaker:Shi Dai
Affiliation：Western Sydney University
Title：Magnetic Field Reversal around
an Active Fast RadioBurst
Abstract：The environment of actively repeating fast radio bursts (FRBs) has been shown to be complex and varying. The recently localized FRB 20190520B is extremely active, has the largest confirmed host dispersion measure (DM), and is only the second FRB source associated with a compact, persistent radio source (PRS). The main tracer of the magneto-ionic environments is the rotation measure (RM), a path-integral of the line-of-sight component of magnetic field strength (B) and electron density, which does not allow a direct probe of the B-field configuration. Here we report direct evidence for a B-field reversal based on the observed sign change and extreme variation of FRB 20190520B’s RM, which changed from +10000 rad/m^2 to -16000 rad/m^2 between June 2021 and January 2022. Such extreme RM reversal has never been observed before in any FRB nor in any astronomical object. The implied short-term change of the B-field configuration in or around the FRB could be due to the vicinity of massive black holes, a magnetized companion star in binary systems, or a young supernova remnant along the line of sight.

Facilitator
-Name：Fujii, Yuka

=============== Mar 1 Wed ===============

Campus：Mitaka,
Seminar：ALMA-J seminar
Regularly Scheduled/Sporadic： Every Wednesday
Date and time： March 1, 2023 (Wed), 14:30 – 15:30
Place： ALMA building #102 / Zoom (hybrid)

Speaker : Hanae Inami and Hiddo Algera
Affiliation: Hiroshima University and NAOJ/Hiroshima University
Title: An ALMA Systematic Survey of Distant Galaxies: Obscured Star Formation at z~7
Abstract:
In recent years, many massive galaxies have been discovered when the Universe was only 1Gyr old or younger. This raises the question of how so much mass was assembled in such a short time. In particular, some of these galaxies are dust rich, suggesting that dust is also being produced in a rapid manner in the early universe. Taking advantage of ALMA’s capability of efficient spectroscopic searches for galaxies at z > 6.5, we have conducted an ALMA Cycle-7 Large Program, REBELS (Reionization Era Bright Emission Line Survey) to perform a systematic study of the interstellar medium (ISM) in 40 UV-selected galaxies at z > 6.5. The design of this survey has allowed us to spectroscopically confirm 23 galaxies in the Epoch of Reionization, as well as detect dust continuum in 14 galaxies, increasing the number of known dusty galaxies at z > 6.5 by a factor of three. In this talk, we will first present an outline of the REBELS program and then focus on discussing recent results from the dust continuum detections. We will present 1) the typical fraction of obscured star formation in UV-selected galaxies at z~7, and 2) new constraints on the dust-obscured cosmic star formation rate density in the epoch of reionization. In addition, we have conducted follow-up observations with ALMA to cover shorter wavelengths in several REBELS galaxies. We will present recent results on the shape of the infrared spectral energy distribution in three z~7 galaxies, and discuss their dust temperatures, masses and ISM properties in the context of the known high-redshift population.

Facilitator: Shun Ishii, Jorge Zavala

=============== Mar 1 Wed ===============

Campus：Mitaka
Seminar：NAOJ Science Colloquium
Regularly Scheduled/Sporadic：Every Wednesday
Date and time：2023 March 1, 15:30-17:00
Place：zoom / Instrument Development Bldg. 3 (hybrid)

Speaker：Mizutani Yohsuke
Affiliation：NAOJ (M2)
Title：TBD
Abstract：TBD

Speaker：Hatano Shun
Affiliation：NAOJ (M1)
Title：TBD
Abstract：TBD

Facilitator
-Name：Akimasa Kataoka
-Comment：English