投稿者: writer

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April 9 Tue 10:00-11:30
太陽系小天体セミナー (Solar System Minor Body Seminar)
Zoom

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April 10 Wed 15:30-16:30
NAOJ Science Colloquium
hybrid; Large Seminar Room in Subaru Building and Zoom

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April 11 Thu 16:00-17:00
NAOJ Seminar
hybrid; Large Seminar Room in Subaru Building and Zoom

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詳細は下記からご覧ください。

=============== April 9 Tue===============

キャンパス：三鷹
セミナー名：太陽系小天体セミナー (Solar System Minor Body Seminar)
定例・臨時の別：定例
日時：　4月　9日（火曜日）　10時00分　～　11時30分
場所：zoom
タイトル：ミーティング

世話人の連絡先
-名前：渡部潤一

備考：zoomでの参加

=============== April 10 Wed===============

Campus: Mitaka
Seminar: NAOJ Science Colloquium
Date and time: 2023 Apr. 10 (Wed.), 15:30-16:30 JST
Place: the large seminar room / Zoom (hybrid)

Speaker: Andris Dorozsmai
Affiliation: NAOJ
Title: Stellar triples with chemically homogeneously evolving inner binaries
Abstract:
Observations suggest that massive stellar triples are common. However, their evolution is not yet fully understood. In this talk, I discuss the evolution of hierarchical triples in which the stars of the inner binary experience chemically homogeneous evolution (CHE), particularly with the aim to explore the role of the tertiary star in the formation of gravitational-wave (GW) sources. To investigate these systems, I use the the triple-star population synthesis code TRES. I found that about 40 per cent of the all triples harboring a CHE inner binary (CHE triples) experience tertiary mass transfer episodes, an event which is rare for classically evolving stars (i.e. non-CHE stars). In the majority of tertiary mass transfer episodes, the accreting inner binary consists of two main sequence stars (58-60 per cent) or two black holes (24-40 per cent). I will also show that von Zeipel-Lidov-Kozai (ZLK) oscillations play an important role in the evolution of these systems. In particular, I find that for triples with initial outers pericentre smaller than 2000 solar radii, ZLK oscillations can result in eccentric (stellar or double compact object) mergers. Approximately 24 per cent of CHE triples become GW sources. Moreover, in a significant fraction of these sources, the tertiary star plays an important role and leads to configurations that are not predicted for isolated binaries. To conclude, the evolution of CHE binaries can be affected by a close tertiary companion, resulting in astronomical transients such as tertiary-driven massive stellar mergers and equal-mass BH-BH binaries that merge via gravitational-wave emission within Myrs.

Facilitator
-Name: Kanji Mori

Comment: English

===============April 11 Thu==============

Campus：Mitaka
Seminar：NAOJ Seminar
Regularly Scheduled/Sporadic：Sporadic
Date and time：April 11, 2024 16:00-17:00
Place：Zoom/Large Seminar Room (hybrid)

Speaker：中島　紀氏
Affiliation：元アストロバイオロジーセンター

Title：干渉計と褐色矮星と量子力学

Abstract: 私の研究生活の中で、4年以上かけた三つの研究対象について
お話しする。第一は、可視域の干渉計イメージングである。当時補償光学は存在せず、どうやって大型望遠鏡の回折限界のイメージイングを行うかは、一つの大きな問題であった。我々は、この問題を、電波の VLBI の手法を応用することで、解決した。
第二は、低温褐色矮星の探索と発見である。探索を始めた当時、褐色矮星は幻の天体であり、探索を行うこと自体に、懐疑的な意見もあった。我々が発見した褐色矮星には、メタンの吸収バンドがあり、それが 1000K 程度の天体であることを決定づけた。
第三は、量子力学の観測の問題である。光子や原子核といったミクロの存在の位置、といったミクロの情報が、我々の存在するマクロの世界の量として観測されるためには、どのようなプロセスを経なければならないか。この問題を現存する検出器の観点から明らかにした。

Facilitator
-Name：Joten Okamoto

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April 5 Fri 16:00-17:00
NAOJ Seminar
hybrid; Large Seminar Room in Subaru Building and Zoom

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詳細は下記からご覧ください。

=============== April 5 Fri===============

Campus：Mitaka
Seminar：NAOJ Seminar
Regularly Scheduled/Sporadic：Regular
Date and time：April 5, 2024 16:00-17:00
Place：Zoom/Large Seminar Room (hybrid)

Speaker：Dr. Chervin Laporte
Affiliation：The Institute of Cosmos Science

Title：The stellar halo as a window on our Galaxy’s formation and dark matter

Abstract:The Galactic stellar halo consists of about 1-2% of the total stellar mass content of the Milky Way. Yet, it provides important clues on the formation of the Galaxy, properties of high redshift galaxies through the study of their resolved stellar populations as well as the nature of dark matter. In this talk, I will introduce the field of near-field cosmology and its goals. I will show how the Gaia mission has helped consolidate our understanding of the formation of the Milky Way but also the nature of dark matter and how numerical simulations are becoming an important tool to interpret observational data and the expected avalanche of data from upcoming spectroscopic/photometric surveys. I will then discuss some of the work we have carried out in our group on the stellar halo, covering the formation history of the Milky Way, interpretation of newly discovered substructures and the interaction of the LMC with the MW through the lens of numerical simulations.

Facilitator
-Name：Joten Okamoto

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March 26 Tue 10:00-11:30
太陽系小天体セミナー
Zoom

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March 27 Wed 15:30-16:30
NAOJ Science Colloquium
hybrid; Lecture room and Zoom

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詳細は下記からご覧ください。

=============== March 26 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26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：DARTによる科学成果とSubaru HSCに期待される太陽系小天体研究
Abstract：DARTミッション(Double Asteroid Redirection Test)は,
NASAが地球防衛のために実施した探査/実験プロジェクト.
二重小惑星システムDidymos-Dimorphosを対象に, 2022年9月26日UTに探査機を衛星Dimorphosに衝突させ,
その軌道を逸らすテストを実施した. 運動量増強係数βは3.61(1σ: +0.19,
-0.25)と見積もられ,数値計算や地上衝突実験による予測値(β=1~6)の範囲内であった.
衛星Dimorphosの公転周期は33±1分短縮され, 軌道長半径は1.21kmから1.17kmへと短くなった.
衝突によって放出されたダストの総質量は~1e7 kg, その大部分を占めたのはboulder
swarmsを含むslow-moving ejecta (>99.5%)であった. 一時的にダブルトレイル構造が観測されたが,
衝突以外のダスト放出メカニズムは確認されず, その見かけは円錐状のイジェクタカ
ーテンに起因する可能性が指摘された. 実際に衝突時以外には衛星Dimorphosの散乱断面積の増大は観測されていない.
DARTミッションにより小惑星軌道変更技術の有効性が実証された. Subaru Hyper Suprime-Cam
(HSC)のデータを用いた既知太陽系小天体の抽出と同定手法は確立されつつある(大坪貴文氏(産業医科大)).
HSCデータから収集された小天体情報は,Minor Planet CenterやNASA/JPL
HORIZONSでの位置情報/観測条件と併せることで軌道情報を取得できる.
各CCDの視野内に小惑星が収まっているかどうかを計算することで効率的な検索アルゴリズムの実装に成功している.
今後は潜在的な地球衝突危険天体の早期発見と追跡にも活用でき,
地球防衛に向けて将来的な小惑星衝突リスク軽減への貢献が期待される.

Refs: DART (Cheng et al. 2023, Nature; Graykowski et al. 2023, Nature; Jewitt et al. 2023, ApJL; Kim & Jewitt 2023, ApJ; Li et al. 2023, Nature; Moreno et al. 2023, PSJ; Thomas et al. 2023, Nature; etc…)

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 27 Wed===============

Campus: Mitaka
Seminar: NAOJ Science Colloquium
Date and time: 2023 Mar. 27 (Wed.), 15:30-16:30
Place: the lecture room / Zoom (hybrid)

Speaker: Laia Barrufet
Affiliation: The University of Edinburgh
Title: HST-dark galaxies: Unveiling the Nature of Infrared Bright, Optically Dark Galaxies with Early JWST Imaging and Spectroscopy
Abstract:
Over the past decade, low-resolution infrared observations have revealed a population of bright IR galaxies undetected with HST, termed “HST-dark galaxies. Nevertheless, their photometric redshifts and physical properties were uncertain due to the limited photometry even including ALMA data. This can result in an incomplete galaxy census at earlier times, due to UV-faint galaxy populations such as quiescent or dust-obscured sources. The key question is: how common are such sources at z >3-4 and what is their contribution to the cosmic star formation rate density? With JWST, we can study for the first time the physical properties of this enigmatic population. In this talk, I will summarise the progress in our understanding of HST-dark galaxies facilitated by JWST data, employing both photometry and spectroscopy. In the first part of the talk, I will expose the progress made with HST-dark galaxies thanks to JWST/NIRcam photometry. I will focus on the results of 30 HST-dark sources selected based on their red colours across 1.6 to 4.4 microns with NIRCam imaging from the Early Release Science Program CEERS. These galaxies are generally highly dust-attenuated, massive, star-forming sources at z~2-8. Our analysis underscores the unique capability of JWST in uncovering this previously elusive galaxy population and in conducting a more complete census of galaxies at z>3 based on rest-frame optical imaging. Interestingly, HST-dark galaxies present a considerable contribution to the obscured star formation rate density at z~7, already in the Epoch of Reionization. In the second part of the talk, I will present the initial NIRSpec spectra of HST-dark galaxies from my GO Cycle-1 program ‘Quiescent or dusty? Unveiling the nature of extremely red galaxies at z>3’. I will showcase spectra for highly attenuated dusty galaxies and quiescent galaxies and their physical characteristics. Despite the prevalence of dust in most galaxies, they exhibit distinct spectral features. Furthermore, HST-dark galaxies harbour hidden gems: quiescent galaxies at redshifts > 3, for which I will present spectra and demonstrate NIRSpec’s capacity to analyze these sources. Finally, I will explore potential avenues for future research involving HST-dark galaxies, leveraging the synergy between JWST and ALMA.

Facilitator
-Name: Haruka Kusakabe

Comment: English