February 20 Tue 10:00-11:30
太陽系小天体セミナー
Zoom
February 20 Tue 16:00-17:00
NAOJ Seminar
hybrid; Lecture room and Zoom
February 21 Wed 14:30-15:30
ALMA-J seminar
hybrid; Room 102 in the ALMA building and Zoom
February 21 Wed 15:30-16:30
NAOJ Science Colloquium
hybrid; Lecture room and Zoom
詳細は下記からご覧ください。
=============== February 20 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：2月20日（火曜日）10時00分～11時30分
場所：zoom
講演者：小林美樹
タイトル：はやぶさ・はやぶさ2光度比較
Abstract：はやぶさ2サンプルリターンカプセルは、当初予想されていた最大光度約－４等級よりも暗い結果となったことを、はやぶさ初号機と比較考慮する。
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
=============== February 20 Tue===============
Campus：Mitaka
Seminar：NAOJ Seminar
Regularly Scheduled/Sporadic：Sporadic
Date and time：February 20, 2024 16:00-17:00
Place：Zoom/Lecture Room (hybrid)
Speaker：Dr. Nicolas Peretto
Affiliation：Cardiff University
Title：On the formation of star clusters in self-gravitating molecular clouds
Abstract:The formation of stellar clusters dictates the pace at which galaxies evolve, and solving the question of their formation will undoubtedly lead to a better understanding of the Universe as a whole. While it is well known that star clusters form within parsec-scale over-densities of interstellar molecular gas called clumps, it is, however, unclear whether these clumps represent the high-density tip of a continuous gaseous flow that gradually leads towards the formation of stars, or a transition within the gas physical properties. Here, I will present a unique analysis of a sample of 27 infrared dark clouds embedded within 24 individual molecular clouds that combine a large set of observations, allowing us to compute the mass and velocity dispersion profiles of each, from the scale of tens of parsecs down to the scale of tenths of a parsec. These profiles reveal that the vast majority of the clouds, if not all, are consistent with being self-gravitating on all scales, and that the clumps, on parsec-scale, are often dynamically decoupled from their surrounding molecular clouds, exhibiting steeper density profiles (ρ∝r-2) and flat velocity dispersion profiles (σ∝r0), clearly departing from Larson’s relations. These findings suggest that the formation of star clusters correspond to a transition regime within the properties of the self-gravitating molecular gas. We propose that this transition regime is one that corresponds to the gravitational collapse of parsec-scale clumps within otherwise stable molecular clouds. I will also present two follow-up studies at high angular resolution that provide direct constraints on how clump collapse proceeds.
Facilitator
-Name：Takashi Moriya
=============== February 21 Wed===============
Campus: Mitaka
Seminar: ALMA-J seminar
Date and time: February 21 (Wed) 14:30-15:30
Place: hybrid (room 102 in the ALMA building and Zoom)
Speaker: Yuhua Liu
Affiliation: Department of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University
Title: Dust Polarization of Prestellar and Protostellar Sources in OMC-3
Abstract:
We present the Atacama Large Millimeter/submillimeter Array (ALMA) observations of linearly polarized 1.1 mm continuum emission at ~0.14” (55 au) resolution and CO (J=2-1) emission at ~1.5” (590 au) resolution towards one prestellar (MMS 4), four Class 0 (MMS 1, MMS 3, MMS 5, and MMS 6), one Class I (MMS 7), and one flat-spectrum (MMS 2) sources in the Orion Molecular Cloud 3 region. The dust disk-like structures and clear CO outflows are detected towards all sources except for MMS 4. The diameters of these disk-like structures, ranging from 16 to 97 au, are estimated based on the deconvolved full width half maximum (FWHM) values obtained from the multi-Gaussian fitting. Polarized emissions are detected towards MMS 2, MMS 5, MMS 6, and MMS 7, while no polarized emission is detected towards MMS 1, MMS 3, and MMS 4. MMS 2, MMS 5, and MMS 7 show organized polarization vectors aligned with the minor axes of the disk-like structures, with mean polarization fractions ranging from 0.6% to 1.2%. The strongest millimeter source, MMS 6, exhibits complex polarization orientations and a remarkably high polarization fraction of ~10% around the Stokes I peak, and 15%-20% on the arm-like structure, as reported by Takahashi et al. (2019). The origins of the polarized emission, such as self-scattering and dust alignment due to the magnetic field or radiative torque, are discussed for individual sources. Some disk-like sources exhibit a polarized intensity peak shift towards the nearside of the disk, which supports that the polarized emission originates from self-scattering.
=============== February 21 Wed==============
Campus: Mitaka
Seminar: NAOJ Science Colloquium
Date and time: 2023 Feb. 21 (Wed.), 15:30-16:30
Place: the lecture room / Zoom (hybrid)
Speaker: Tatsuya Matsumoto
Affiliation: Kyoto University
Title: Effects of internal heating sources on hydrogen-rich supernova light curves
Abstract:
Core-collapse supernovae (SNe) are caused by the death of massive stars, and their light curves provide a lot of information about the stellar evolution and physical processes of explosions. In particular, the light curves of hydrogen-rich SNe have a characteristic slowly-evolving phase, so-called the plateau phase, whose luminosity and duration are related to the SN parameters such as ejecta mass and energy. Recent observations revealed that some H-rich SNe exhibit evidence for a sustained energy source powering their light curves, resulting in a brighter and/or longer-lasting plateau phase.
We present a semi-analytic light curve model that accounts for the effects of an arbitrary internal heating source such as 56Ni/Co decay, a central engine (millisecond magnetar or accreting compact object), and shock interaction with a dense circumstellar disk.
While a sustained internal power source can boost the plateau luminosity commensurate with the magnitude of the power, the duration of the recombination plateau can typically be increased by at most a factor
∼2−3 compared to the zero-heating case. For a given ejecta mass and initial kinetic energy, the longest plateau duration is achieved for a constant heating rate at the highest magnitude that does not appreciably accelerate the ejecta. This finding has implications for the minimum ejecta mass required to explain particularly long-lasting supernovae, and for confidently identifying rare explosions of the most-massive hydrogen-rich (e.g. population III) stars.
Facilitator
-Name: Koh Takahashi
Comment: English