2月27日（月）13：30～15：00 太陽系小天体セミナー 南棟２階会議室
Feb 27 mon Solar System Minor Body Seminar Conference Room, South Bldg.2F
3月1日（水）13：30～14：30 理論コロキウム 輪講室
Mar 1 wed DTA colloquium Rinkoh seminar room
3月3日（金）13：30～15：00 太陽天体プラズマセミナー 院生セミナー室
Mar 3 fri Solar and Space Plasma Seminar Student Seminar Room, Subaru Bldg.
3月3日（金）16：00～17：00 国立天文台談話会 大セミナー室
Mar 3 fri NAOJ Seminar Large Seminar Room
詳細は以下をご覧下さい。
2月27日（月）
- 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27日（月曜日）13時30分～15時
- 場所
- 南棟２階会議室
- 講演者
- 臼井文彦
- 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
3月1日（水）
- Campus
- Mitaka
- Seminar
- DTA colloquium
- Regularly Scheduled/Sporadic
- Regularly Scheduled Date and time：01 March 2016, 13:30-14:30
- Place
- Rinkoh seminar room
- Speaker
- Tatsuya Satsuka
- Affiliation
- Osaka University
- Title
- Evolution of binary seeds in collapsing protostellar cloud
- Abstract
- It is widely recognized that the majority of main-sequence stars and pre-main-sequence stars are in binary systems and that these binaries have various distributions in mass ratio q, binary separation, and binary frequency. The seed binaries are considered to form via fragmentation process. After the fragmentation, the seed binary start to accrete the surrounding envelope and grow towards main-sequence stars. In order to understand the distributions of binaries, we need to investigate the evolution of binaries from seeds to stars. Previous works have studied the gas accretion on to binary assuming constant angular momentum and density of gas at the outer boundary. However, these distributions of gas density and gas angular momentum are unrealistic incollapsing protostellar cloud. We perform 3D smoothed particle hydrodynamics (SPH) simulations of gas accretion on to the seeds of binary stars to investigate their short-term evolution. Taking into account the dynamically evolving envelope with non-uniform distribution of gas density and angular momentum of accreting flow, our initial condition includes a seed binary and a surrounding gas envelope, modelling the phase of core collapse of gas cloud when the fragmentation has already occurred. We run multiple simulations with different values of initial mass ratio q0 (the ratio of secondary over primary mass) and gas temperature. For our simulation setup, we find a critical value of qc = 0.25 which distinguishes the later evolution of mass ratio q as a function of time. If q0 > qc, the secondary seed grows faster and q increases monotonically towards unity. If q0 qc evolves towards an equal-mass binary star and that with q0 < qc evolves to a binary with an extreme value of q. Binary separation is a monotonically increasing function of time for any q0, suggesting that the binary growth by accretion does not lead to the formation of close binaries.
- Facilitator
- -Name：Tomoya Takiwaki
- Comment
- in English
3月3日（金）
- Campus
- Mitaka
- Seminar
- Solar and Space Plasma Seminar
- Regularly Scheduled/Sporadic
- Regular
- Date and time
- 3 March (Fri), 13:30-15:00
- Place
- Student Seminar Room, Subaru Bldg.
- Speaker
- Takayoshi Oba
- Affiliation
- SOKENDAI/ISAS/JAXA
- Title
- The photospheric structure of granules retrieved by a deconvolution technique applied to Hinode/SP
- Abstract
-
The solar granulation is a manifestation of convective motions in the photosphere. Hot gas material ascends into the photosphere, forming the bright feature of granules. Subsequently, it is cooled by the radiative energy release and descends, making intergranular lanes. Many observational works in the past have found stronger upflows in granules and weaker downflows in intergranular lanes. However, this trend is not compatible with the prediction provided by numerical simulations, in which the downflow becomes stronger to keep the mass conservation in the photosphere. One possibility to cause this discrepancy is the non-perfection in the imaging performance of a telescope, which mixes the upward velocity signals and downward ones. Accordingly, we develop a deconvolution technique that corrects this imaging performance and recover an original image, using the spectral data observed with the spacecraft Hinode under the perfect lack of the atmospheric-seeing effect. Our study found a significant enhancement for the convective velocity fields of both upflow and downflow, reaching values of -3.0
(upward) and +3.0 km/s (downward); this amplitude is remarkably higher than that from -2.0 to +1.5 km/s derived in the spectral data before the deconvolution. The obtained magnitude relation approaches to that reproduced by numerical simulations due to the preferential enhancement in the downflow. Our deconvolution technique not only improve the amplitude of the velocity field but also significantly affect their morphology. The area of intergranular downflows remarkably increases through the deconvolution; the upflows in the edge of each granule transforms to downflows, and narrow intergranular channels sandwiched by granules appear or broaden their width. Our results, thus, suggest that an appropriate deconvolution needs to be done for deriving the amplitude of the convective velocity field and to investigate the convective dynamics in tiny scale, in particular, the narrow intergranular lanes. - Facilitator
- -Name：Shin Toriumi
3月3日（金）
- キャンパス
- 三鷹
- セミナー名
- 国立天文台談話会
- 定例・臨時の別
- 定例
- 日時
- 3月3日（金） 16:00-17:00
- 場所
- 大セミナー室
- 講演者
- 水本好彦
- 所属
- 国立天文台天文データセンター
- タイトル
- 「国立天文台での22年 – やろうとしたこと、できなかったこと」（退官記念講演）
- Abstract
-
定年を前にして国立天文台での22年間をふり返ると多かれ少なかれ、すばる望遠鏡に関連した仕事をしてきた。すばる望遠鏡の建設にあたり多くの
人たちが「何か新しいことができるんじゃないか」と燃えていた時代に私も参加できたのは幸運だった。やりたいことが実現できるという期待が
徐々に幻想に変わっていくのが時の流れ。そのなかではやろうとしてできなかったことが棘のように刺さって記憶に残る。談話会ではこの棘を抜い
て次の世代への置き土産にしたいと思う。 - 連絡先
- -名前：久保 雅仁
以上