2月12日（水）13:30～15:00 科学研究部コロキウム 開発棟３号館３階セミナー室
Feb 12 Wed Colloquium of Division of Science Conference room,Instrument Development Bldg.3 3F
2月13日（木）12:00～ ALMA-J セミナー アルマ棟 1階 102
Feb 13 Tur ALMA-J Seminar ALMA building Room 102
2月14日（金）13:30～15:00 太陽天体プラズマセミナー すばる棟院生セミナー室
Feb 14 Fri Solar and Space Plasma Seminar Student Seminar Room, Subaru Bldg.
2月14日（金）15:00～ 太陽系科学セミナー 輪講室
Feb 14 Fri Solar System Science Seminar Rinko Room
詳細は以下をご覧下さい。
2月12日（水）
- キャンパス
- 三鷹
- セミナー名
- 科学研究部コロキウム
- 定例・臨時の別
- 定例
- 日時
- 2月 12日（水曜日） 13時30分 ～ 15時
- 場所
- 開発棟３号館３階セミナー室
- 講演者
- 岡本 崇
- 所属
- 北海道大学
- タイトル
- 銀河形成におけるフィードバックの役割
- 連絡先
- -名前：片岡章雅
- 備考
- 使用する言語は英語
2月13日（木）
- Campus
- Mitaka
- Seminar
- ALMA-J Seminar
- Regularly Scheduled/Sporadic
- Regularly Scheduled Date and time：Thursday, February 13 at 12pm
- Place
- room 102 in ALMA building
- Speaker
- Patricio A. Sanhueza Nunez
- Affiliation
- NAOJ
- Title
- The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES)
- Abstract
- The ALMA Survey of 70 μm dark High-mass clumps in Early Stages (ASHES) is designed to systematically characterize the earliest stages and constrain theories of high-mass star formation. Twelve massive, cold, 3.6─70 μm dark prestellar clump candidates, embedded in IRDCs, were carefully selected in the pilot survey to be observed with ALMA. We have mosaicked each clump (?1 arcmin2) in continuum and line emission with the 12 m, 7 m, and TP arrays at 224 GHz (1.34 mm), resulting in ?1.″2 resolution (?4800 au). We detect 294 cores, from which 84 (29%) are categorized as protostellar based on outflow activity or “warm core” line emission. The remaining 210 (71%) are considered prestellar core candidates. The number of detected cores is independent of the mass sensitivity range of the observations and, on average, more massive clumps tend to form more cores. We find a large population of low-mass (30 Msun) prestellar cores (maximum mass 11 Msun ). From the prestellar core mass function, we derive a power-law index of 1.17 ± 0.10, which is slightly shallower than Salpeter. We used the minimum spanning tree (MST) technique to characterize the separation between cores and their spatial distribution, and to derive mass segregation ratios. While there is a range of core masses and separations detected in the sample, the mean separation and mass per clump are well explained by thermal Jeans fragmentation and are inconsistent with turbulent Jeans fragmentation. Core spatial distribution is well described by hierarchical subclustering rather than centrally peaked clustering. There is no conclusive evidence of mass segregation. We test several theoretical conditions and conclude that overall, competitive accretion and global hierarchical collapse scenarios are favored over the turbulent core accretion scenario.
- Facilitator
- -Name：Dieu Nguyen and Junko Ueda
2月14日（金）
- Campus
- Mitaka
- Seminar
- Solar and Space Plasma Seminar
- Regularly Scheduled/Sporadic
- Regular
- Date and time
- 14 February (Fri), 13:30-15:00
- Place
- Student Seminar Room, Subaru Bldg.
- Speaker
- Masanori Iwamoto
- Affiliation
- The University of Tokyo
- Title
- Synchrotron Maser Emission and Associated Particle Acceleration in Relativistic Shocks
- Abstract
-
The acceleration mechanism for generating ultra-high-energy cosmic rays (UHECRs) with energies above 10^18eV is one of the most important unsolved problems in astrophysics. Relativistic shocks in extragalactic astrophysical objects such as jets from active galactic nuclei (AGNs) and gamma-ray bursts (GRBs) are considered as efficient acceleration sites and commonly proposed sources for UHECRs. Observations of anisotropy in the arrival direction of the UHECRs favor the extragalactic origin.
In relativistic shocks, large-amplitude electromagnetic waves are excited by synchrotron maser instability (SMI) in the shock transition and propagate upstream (Hoshino & Arons 1991). The precursor wave emission via the SMI is widely studied by means of 1D particle-in-cell (PIC) simulations. Hoshino (2008) demonstrated that the pump electromagnetic wave decays into a Langmuir wave via parametric decay instability and found that nonthermal particles are generated in the manner analogous to wakefield acceleration (WFA) during the nonlinear process of the Langmuir wave collapse. The WFA is first proposed in laboratory plasmas (Tajima & Dawson 1979) and recently applied for UHECR acceleration (e.g., Chen et al. 2002). The WFA in the context of relativistic shocks is considered a promising candidate for UHECR acceleration.
It was believed that in multidimensional shocks, the intense wave emission via the SMI would cease soon due to inhomogeneity along the shock surface. Recently, however, our high-resolution 2D PIC simulations in pair plasmas showed that the wave emission continues (Iwamoto et al. 2017, 2018). Although our studies give positive results for the WFA in relativistic shocks, we could not directly demonstrate it because finite mass difference of two opposite charges is essential for exciting the wakefield.
In this presentation, by performing 2D PIC simulation of ion-electron shocks, we will demonstrate that the wakefield is indeed induced by the large-amplitude precursor wave. Especially for relatively high magnetization, the precursor wave amplitude is significantly amplified and exceeds that in pair plasmas due to a positive feedback process associated with ion-electron coupling through the wakefield. Nonthermal electrons and ions are generated during the nonlinear process of the wakefield collapse and the particle energy spectrum shows a power-law distribution. We will discuss the particle acceleration mechanism in details. - Facilitator
- -Name：Munehito Shoda
2月14日（金）
- キャンパス
- 三鷹
- セミナー名
- 太陽系科学セミナー
- 定例・臨時の別
- 定例
- 日時
- 2月14日（金曜日）15時00分～
- 場所
- 輪講室
- 講演者
- 吉田二美
- 所属
- 千葉工業大学
- タイトル
- ケンタウルスについて我々が今知っていること、これからやるべき事
- Abstract
- 1977年にChironが発見され、木星と海王星の間にも小天体がいること
がわかった。
それから40年余り、現在知られているケンタウルスの数は300個ほどである。
彗星活動を示すもの、リングを持つもの、太陽系で最も赤い天体、バイナリー
等、ケンタウルスはバラエティに富むメンバーで構成されている。
またケンタウルスは、力学的にはオールト雲またはTNOからJFCへ遷移する過程に
ある天体と考えられており、スノーラインの外側で形成された氷天体の物理的・
化学的進化を追う上で重要な天体群である。
ケンタウルスは遠くて暗いため、現在もなお未発見の天体が多く存在すると思わ
れる。
だが2020年代にLSSTによる全天サーベイが始まれば、もっと多くのケンタウルス
が発見されるだろう。
この発表では、現時点でのケンタウルスに関する我々の知識をまとめ、今後私た
ちがどのような観測（あるいは実験、シミュレーション）を行えばケンタウルス
を通じて太陽系形成に関する理解が深まるかを議論する。 - 連絡先
- -名前：樋口有理可
- 備考
- テレビ会議による参加も可