Jun 22 Tue 10:00～11:30 太陽系小天体セミナー / Solar System Minor Body Seminar zoom
Jun 23 Wed 15:00 ～16:00 ALMA-J seminar zoom
Jun 23 Wed 15:30～17:00 NAOJ Science Colloquium zoom
Jun 25 Fri 13:30～15:00 Solar and Space Plasma Seminar zoom
Jun 25 Fri 16:00～17:00 談話会 / NAOJSeminar zoom
詳細は以下をご覧下さい
6月22日（火）
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：6月22日（火曜日）10時00分～11時30分
場所：zoom
講演者：紅山仁
所属：東大天文センター
タイトル：木曽Tomo-e Gozenを用いた微小地球接近小惑星の高時間分解撮像観測
Abstract：近日点距離が1.3 au未満で定義され地球に接近する軌道を持つ小惑星
を地球接近小惑星(Near Earth Objects, NEO)という。NEOの多くは火星–木星間
のメインベルト小惑星が軌道進化した天体であり、その軌道進化過程においては
太陽の輻射に起因して小惑星の軌道や自転状態が変化する非重力効果が重要とな
る。非重力効果の一つで自転周期を変化させるYORP効果は直径の2乗に反比例す
る強いサイズ依存性をもち、軌道進化に比べて短いタイムスケールで微小天体の
自転周期を変化させる。太陽系内の物質輸送を担うNEOの力学史の解明には非重
力効果の理解が不可欠であるが、YORP効果の観測的検出は数例しかなく未解明な
点が多い。
YORP効果による自転加速を受け構造を維持できなくなった天体は変形や自転破壊
を経験するため、YORP効果が強く働く微小NEOの自転周期分布は力学史や強度を
反映した物理量である。近年、微小NEOでは1分以下の高速自転が検出されており
正確な自転周期の推定には高速撮像観測が必要となる。そこで我々は東京大学木
曽観測所105 cmシュミット望遠鏡に搭載されたTomo-e Gozenカメラを用いた2fps
観測により、推定直径3–86 m の51天体の微小NEOの高時間分解光度曲線を取得
した。計32天体の微小NEOの自転周期と軸比(形状)を推定し、周期20秒以下の高
速自転小惑星を7天体発見した。本発表では光度曲線、軸比、自転周期などの観
測結果を紹介した後、系統的な高速観測で得た微小NEOの自転周期分布の解釈を
行う。
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
6月23日（水）
Campus: Mitaka
Seminar: ALMA-J seminar
Regularly Scheduled/Sporadic: Every Wednesday
Date and Time: 2021 June 23 15:00-16:00
Place: Zoom
Speaker：Yiping Ao (Purple Mountain Observatory)
Title: Searching for cooling flows
Abstract: Gas plays an important role in galaxy formation and evolution. However, it is still unclear how molecular gas forms in the central galaxies of galaxy clusters, and how high-redshift galaxies accreting materials form their interstellar medium. With studies of observations towards galaxies in the local Universe and at high redshifts, we try to understand how galaxies get gas mass. As we know, there is a large amount of hot gas around galaxy clusters revealed by X-ray observations. Although suffering the cooling flow problem, cold gas has been found in many clusters with the cooling rate much lower than the standard cooling flow model. However, the origin of cold gas is not clear. We would like to carry out a sensitive HI survey with FAST in a pilot sample of X-ray selected clusters. These results, together with the gas phase revealed at other wavelengths, might provide us the clue on cold gas formation in these system. Cosmological simulations show that gas accretion is important for galaxy formation at high redshift, and we should observe gas infall at this epoch. Such evidence is rare, though. The heating mechanism of Lyman alpha blobs is still unclear and debated. The extended Lyman alpha emission may be linked to the process of galaxy formation at early epochs. Cooling flows are very likely to be detected in such objects, and we have such an example from our recent work. We would like to search for evidence of such flows around Lyman alpha blobs with less SFR, where feedbacks are weak, by investigating the line profiles of the ionized gas around them. This will help us to understand galaxy formation and evolution at high redshifts. We will present some preliminary results based on our recent ALMA and VLT data.
Facilitator: Yuichi Matsuda, Yusuke Miyamoto
6月23日（水）
Campus：Mitaka
Seminar：NAOJ Science Colloquium
Regularly Scheduled/Sporadic：Every Wednesday
Date and time：2021 June 23, 15:30-17:00
Place：zoom
Speaker：David Ehrenreich
Affiliation：Université de Genève
Title：The most extreme climates in the Universe
Abstract：Planets around other stars ―exoplanets― showcase an amazing diversity. This diversity offers many opportunities to study phenomena that do not occur on our Solar System planets, but which may have occured in the past, or could occur in the future. Ultrahot gas giants offer such an opportunity: these are exoplanets so close to their hot stars that they receive thousands of time the insolation of Earth. As such, they are extreme laboratories to study atmospheric physics, chemistry, and climates. They are also well amenable to remote sensing by space-borne and ground-based observations. Trying to learn more about the most extreme climates in the Universe, we could measure stellar dayside temperatures, metallic rains on the nightsides, and atmospheric escape so strong that it may sculpt the whole population of close-in planets. We have also been using these outstanding exoplanets as trojan horses to benchmark characterization techniques that could eventually be applied to smaller, milder planets. I will discuss some of the recent results my group has obtained exploiting data from a range of space-borne and ground-based instruments.
Facilitator
-Name：Akimasa Kataoka
Comment：English
6月25日（金）
Campus： Mitaka
Seminar： Solar and Space Plasma Seminar
Regularly Scheduled/Sporadic： Scheduled
Date and time：25 June (Fri), 13:30-15:00
Place： zoom
Speaker：Ryouhei Nakatani
Affiliation： Riken
Title：Revisiting the Underlying Physics for Photoevaporation of Protoplanetary Disks: Towards Generic UnderstandingAbstract：
In a variety of astrophysical problems, we find a situation where a clump of gas is irradiated by ultraviolet and X-ray from radiation sources. An important outcome of this process is that excessive photon energy goes into the heat for the gas, which results in driving winds. This wind-driving process, termed photoevaporation, is essential to determine the fate of the irradiated objects. Protoplanetary disks are one of such objects. The stellar UV and X-ray can yield sufficiently high mass-loss rates that can disperse the disks within 10Myr. The basics of this physical process is, however, not sufficiently understood yet. To address the issue, we have recently developed an analytic model for photoevaporation in a first-principles approach. It is of use to understand the basic physics operating in the vicinity of the wind-launching points. In this talk, I present the analytic model. I also reivew long-standing issues remaining in the field; I think collaborative studies between “disk researchers” and “star researchers” are essential to solve them.
Facilitator
-Name：Munehito Shoda
6月25日（金）
Campus：Mitaka
Seminar：NAOJ Seminar
Regularly Scheduled/Sporadic：Scheduled
Date and time：2021 June 25, 16:00～17:00
Place：zoom
Speaker：石垣 美歩 / Ishigaki, Miho
Affiliation： 国立天文台ハワイ観測所 / Subaru Telescope,NAOJ
University of California, Berkeley / Kavli IPMU, the University of Tokyo
Title：Probing the origin of metals in the early Universe with ancient stars in the Milky Way
Abstract：
Metals (elements heavier than H and He) have played an important role in setting the scene for the biggening of the galaxy formation and the matter production in the cosmic history. Atmospheric chemical compositions of ancient stars in our Milky Way Galaxy provide observational probes of physical properties of stars and supernova explosions that were responsible for producing metals at the time of their birth. In this talk, I will present our studies on the implications of observed chemical compositions in old metal-poor stars on the physical properties of the first generations of stars and supernovae, making use of theoretical core-collapse and Type Ia supernova yield models. I will then discuss future prospects of finding old metal-poor stars in the unexplored outer part of the Milky Way halo with the wide-field instruments, HSC and PFS, on Subaru and of follow-up spectroscopic studies with TMT.
Facilitator
-Name：尾崎 忍夫 / Ozaki, Shinobu