2月25日（火）13:30～15:00 太陽系小天体セミナー 南棟２階会議室
Feb 25 Tue Solar System Minor Body Seminar Conference Room, South Bldg.2F
2月26日（水）13:30～ NAOJ Science Colloquium 開発棟３号館３階会議室
Feb 26 Wed NAOJ Science Colloquium Conference Room, Instrument Development Bldg. 3 3F
2月26日（水）15:00～17:00 談話会 大セミナー室
Feb 26 Wed NAOJ Seminar Large Seminar Room
2月27日（木）12:00～ ALMA-J セミナー アルマ棟 1階 102
Feb 27 Thu ALMA-J Seminar ALMA building Room 102
2月28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 28 Fri Solar and Space Plasma Seminar Student Seminar Room, Subaru Bldg.
2月28日（金）16:00～17:00 談話会 大セミナー室
Feb 28 Fri NAOJ Seminar Large Seminar Room
詳細は以下をご覧下さい。
2月25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
- 2月25日（火曜日）13時30分～15時
- 場所
- 南棟２階会議室
- 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
2月26日（水）
- Campus
- Mitaka
- Seminar
- NAOJ Science Colloquium
- Regularly Scheduled/Sporadic
- Regularly Scheduled
- Date and time
- Feb 26 (Wed) 13:30-
- Place
- Conference Room, Instrument Development Bldg. 3 3F
- Speaker
- Tomoyuki Hanawa
- Affiliation
- Chiba University
- Title
- A Proper Discretization of Hydrodynamical Equations in the Cylindrical Coordinates for Astrophysical Simulations
- Abstract
-
The cylindrical coordinates are often used in computational fluid dynamics, in particular, when one considers gas flow accreting onto a central object. Although the cylindrical coordinates have several advantages in describing rotation, they have apparent singularity along the axis at the coordinate origin, i.e., the z-axis. This singularity introduce difficulties in numerical simulations. First, it is difficult to reproduce the flow across the z -axis.
Second, the time step is extremely shortened by the CFL condition near the z-axis since the numerical cell thereof is narrow in the azimuthal direction for a given angular resolution.
Here, we propose a new discretization scheme to overcome these difficulties.
In our new scheme, we take account of change in the direction of the unit vector within a cell when evaluating the flux across each cell surface. In addition, we evaluate the source term in the radial component of the momentum equation from the thermal and dynamical pressures working on the azimuthal cell surface. The new scheme is designed to be free stream preserving so that a flow with uniform density, pressure and velocity is an exact solution of the discretized equation. These improvements are essential to use a lower angular resolution innermost area, and thus to elongate each time step. Our examples demonstrate that the innermost circular region around the axis can be resolved by only six numerical cells.
The angular resolution is higher at a larger radial distance so that each numerical cell has an aspect ratio close. Then the CFL condition is relaxed.
We present an application to an accreting compact star surrounded by a disk in addition to
Sod shock tube and rotating outflow tests. These test problems indicate that accuracy
and stability are greatly improved. - Facilitator
- -Name：Akimasa Kataoka
2月26日（水）
- Campus
- Mitaka
- Seminar
- NAOJ seminar
- Regularly Scheduled/Sporadic
- Scheduled
- Date and time
- Wednesday, Feb 26 15:00-17:00
- Place
- Large Seminar Room
- Speaker
- Richard Tresch Fienberg
- Affiliation
- Press Officer of the American Astronomical Society
- Title
- “Education & Outreach at the American Astronomical Society”
- Abstract
- The American Astronomical Society (AAS), established in 1899, is the major organization of professional astronomers in North America. The membership (approx. 8,000) also includes physicists, mathematicians, geologists, engineers, and others whose research interests lie within the broad spectrum of subjects now comprising the astronomical sciences. The mission of the AAS is to enhance and share humanity’s scientific understanding of the universe, which it achieves through publishing, meeting organization, education and outreach, policy advocacy, and training and professional development. Here we’ll focus on education and outreach, emphasizing programs such as workshops at AAS meetings, the promotion of professional-amateur collaboration, the recent acquisition of Sky & Telescope, and outreach and advocacy related to the controversy over the future of astronomy on Maunakea and threats to astronomy posed by megaconstellations of communication satellites in low Earth orbit.
- Speaker
- Lars Lindberg Christensen
- Affiliation
- Head of Communications, Education & Engagement, NSF’s AstroLab, USA
- Title
- “AstroLab and the current evolution of US ground-based astronomy”
- Abstract
- We live in the most exciting age of astronomical discovery. The US arguably leads the field of space-based astronomy, but some say that in the field of ground-based astronomy the US is slipping behind. A new exciting initiative has just been launched to stimulate development and create new synergy in this area. All National Science Foundation (NSF) optical observatories have been combined into one ? NSF’s National Optical-Infrared Astronomy Research Laboratory, or AstroLab. The new organization operates five scientific programs: Cerro Tololo Inter-American Observatory, the Community Science and Data Center, Kitt Peak National Observatory (all formerly known as the National Optical Astronomy Observatory); Gemini Observatory and the upcoming Large Synoptic Survey Telescope, and is managed by the Association of Universities for Research in Astronomy (AURA).
- Facilitator
- -Name：Kataoka, Akimasa
2月27日（木）
- Campus
- Mitaka
- Seminar
- ALMA-J Seminar
- Regularly Scheduled/Sporadic
- Regularly Scheduled Date and time：Thursday, February 27 at 12pm
- Place
- room 102 in ALMA building
- Speaker
- Yoshito Shimajiri
- Affiliation
- NAOJ
- Title
- Witnessing the fragmentation of filaments into prestellar cores in Orion B/NGC2024
- Abstract
- Recent Herschel observations of nearby molecular clouds revealed that filamentary structures are ubiquitous and that most prestellar cores form in dense filaments. Thus, revealing that the dense filaments are fragmenting into cores from the kinematic viewpoint observationally is crucial to understand the star formation in filaments. In order to investigate whether the observed filaments are fragmenting into cores, we observed NGC2024 of the Orion B molecular cloud in the 12CO (J=1-0), 13CO (J=1-0), C18O (J=1-0), and H13CO+ (J=1-0) molecular lines with Nobeyama 45m telescope and in H13CO+ (J=1-0) with NOEMA. The distributions of the 13CO, C18O, and H13CO+ emission show the filamentary structure. The mean radial column density profile in Herschel shows the 0.064±0.014 pc filament width which is consistent with the previous Herschel studies. On the other hand, the widths of the filamentary structures traced in 13CO and C18O are larger than that in Herschel, while the width in H13CO+ is narrower. These results suggest the 13CO and C18O emission trace only the outer (lower density) part of the Herschel filament and the H13CO+ emission traces only the inner (denser) part. To identify cores embedded in the filament, we performed the dendrogram analysis on the Herschel column density and NOEMA H13CO+ cube maps. As a result, we detected four cores in the Herschel map toward the area covered with the NOEMA and found that each core detected in Herschel corresponds to one core detected in the NOEMA H13CO+ cube map. The Nobeyama H13CO+ centroid velocity map shows the velocity gradient along both axes of the filament and velocity oscillation with period λ -0.2 pc along the major axis. A comparison between centroid velocity and density distributions revealed that there is a tentative λ/4 phase shift between two distributions around the core associated with a protostar. The velocity structure function of our toy model of the fragmenting filament also has a good agreement with the observed velocity structure function. These results can be explained that the filament in NGC2024 fragments into cores.
- Facilitator
- -Name：Dieu Nguyen and Junko Ueda
2月28日（金）
- Campus
- Mitaka
- Seminar
- Solar and Space Plasma Seminar
- Regularly Scheduled/Sporadic
- Regular
- Date and time
- 28 February (Fri), 13:30-15:00
- Place
- Student Seminar Room, Subaru Bldg.
- Speaker
- Sara Tomita
- Affiliation
- Aoyama Gakuin University
- Title
- The Weibel mediated shocks propagating into an inhomogeneous plasma
- Abstract
-
Gamma-ray bursts (GRBs), which are the most luminous electromagnetic explosions in the universe, release relativistic jets, and they are followed by a long-lived afterglow.
Observations of GRB afterglows suggest that downstream magnetic fields are strongly amplified to about 100 times the shock-compressed value in the large downstream region of the relativistic shock. The Weibel instability generates magnetic fields in a collisionless plasma with anisotropic temperature, which is thought to be a crucial role for particle acceleration and magnetic field generation in relativistic collisionless shocks. Recent simulations of collisionless shocks in homogeneous plasmas suggest that the magnetic field generated by the Weibel instability decays rapidly, which cannot explain observed properties of afterglows of GRBs. However, there really must be density fluctuations in interstellar/circum-burst media. In this seminar, I’d like to talk about the result of two-dimensional Particle-In-Cell (PIC) simulations of relativistic unmagnetized collisionless shocks propagating into an inhomogeneous plasma. - Facilitator
- -Name：Munehito Shoda
2月28日（金）
- Campus
- Mitaka
- Seminar
- NAOJ seminar
- Regularly Scheduled/Sporadic
- Scheduled
- Date and time
- Friday, Feb 28 16:00-17:00
- Place
- Large Seminar Room
- Speaker
- 相馬 充
- Affiliation
- 国立天文台 科学研究部
- Title
- 【退職記念講演】「1980年代以降，食予報はいかに精密になってきたか」
- Abstract
-
月・惑星の暦や恒星の位置精度は1980年代以降，飛躍的に向上した．
月・惑星については，レーザーやレーダー観測，恒星については
Hipparcos星表の寄与が大きい．それが顕著に表れるのは，掩蔽観測で
あり，特に恒星が月の縁すれすれをかすめる接食がかなり正確に
予報できるようになった．この予報には，日本の月周回衛星「かぐや」
が測定した月の地形の寄与も大きい．これにより，月縁の凹凸を
考慮した皆既日食や金環日食の予報も正確に行うことができるように
なった．また，ヨーロッパ宇宙機関 ESA による最新の Gaia DR2 の
データの利用により，小惑星による掩蔽の予報も正確に行えるように
なり，昨年には，わずか直径 5km ほどの小惑星 Phaethon による掩蔽の
観測にも成功した．しかし，接食の観測からは Gaia DR2 のデータにも
誤差があることが明らかになっている．これらの点についてお話しする． - Facilitator
- -Name：Kataoka, Akimasa