カテゴリー: 国立天文台談話会

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

February 13 Tue 10:00-11:30
太陽系小天体セミナー
Zoom

February 13 Tue 11:00-12:00
SOKENDAI Doctoral Thesis Preliminary Evaluation
hybrid; Large Seminar Room in Subaru Building and Zoom

February 14 Wed 14:30-15:30
ALMA-J seminar
hybrid; Room 102 in the ALMA building and Zoom

February 14 Wed 15:30-16:30
NAOJ Science Colloquium
hybrid; Lecture room and Zoom

February 16 Fri 16:00-17:00
NAOJ Seminar
hybrid; Large Seminar Room in Subaru Building and Zoom

詳細は下記からご覧ください。

=============== February 13 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13日（火曜日）10時00分～11時30分
場所：zoom
講演者：有松 亘
タイトル：中・大型太陽系外縁天体による恒星掩蔽キャンペーン観測の現状
Abstract：既知の太陽系外縁天体による恒星掩蔽イベントの観測は、外縁天体のサイズ・形状の決定、および衛星や環、表面大気への制約を得るうえで極めて有用である。本発表では現在国内の複数の観測装置を用いて実施している外縁天体恒星掩蔽キャンペーン観測の現状を報告する。

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 13 Tue ===============

Campus：Mitaka
Seminar：SOKENDAI Doctoral Thesis Preliminary Evaluation
　　　　 総研大博士学位論文予備審査会
Regularly Scheduled/Sporadic：Sporadic
Date and time：February 13, 2024　11:00～12:00

Place : Large Seminar Room and Zoom

Speaker：Yuta Tashima
Title：Elucidation of galactic magnetic field structure by pseudo-observation focusing on depolarization

Facilitator
-Name：Nozomu Tominaga, Hideyuki Kobayashi, Natsuko Fujii (Graduate Student Affairs Unit)

=============== February 14 Wed===============

Campus: Mitaka
Seminar: ALMA-J seminar
Date and time: February 14 (Wed) 14:30-15:30
Place: hybrid (room 102 in the ALMA building and Zoom)

Speaker: Yulong GAO
Affiliation: School of Astronomy and Space Science, Nanjing University, Nanjing, China
Title: Unraveling the Low-Metallicity Merging Dwarf Galaxies: Insights into Starburst and Metal Dilution/Enrichment

Abstract:
Understanding the physical mechanisms driving starbursts within dwarf galaxies remains a challenge in astrophysics. Moreover, the impact of mergers on star formation activity in these galaxies remains unclear. In this talk, we employ observations from the VLT/MUSE and ALMA to investigate how the merger process influences star formation activities in metal-poor dwarf galaxies, focusing on galaxies of Haro 11 and NGC 4809/4810. Haro 11, situated in the late-stage merger phase, exhibits similar morphology and kinematics to the Antennae galaxy, offering valuable insights into the merger-induced starburst phenomenon. Conversely, the ongoing collision between NGC 4809 and NGC 4810 presents a unique opportunity to examine the effects of mergers on dwarf galaxies in real time, particularly within their overlapping regions. We find post-merger between low mass galaxies (e.g., Haro 11) can trigger global starburst, similar to ULIRGs. Notably, Haro 11 could be the analog of high-z dwarf starbursts and the potential progenitor of the nearby less massive elliptical galaxies. Furthermore, we find that NGC 4809/4810 interaction zone show enhanced SFR (sSFR), and deficient metallicity, indicating the capacity of dwarf galaxy mergers to instigate significant star formation activity even within metal-poor environments. Additionally, we detect clear evidence of metal enrichment resulting from the Type Ic SN 2011jm within NGC 4809, representing a pioneering detection of chemical pollution through stellar feedback beyond the Local Volume. These findings shed light on the underlying mechanisms driving starburst and stellar feedback processes within the dwarf galaxies.

=============== February 14 Wed==============

Campus: Mitaka
Seminar: NAOJ Science Colloquium
Date and time: 2023 Feb. 14 (Wed.), 15:30-16:30
Place: the lecture room / Zoom (hybrid)

Speaker: Ryota Kitamura
Affiliation: The University of Tokyo (M1)
Title: Review on Pan et al. (2022) “The terrestrial planet formation around M dwarfs: in situ, inward migration, or reversed migration”
Abstract of the paper:
Terrestrial planets are commonly observed to orbit M dwarfs with close-in trajectories. In this work, we extensively perform N-body simulations of planetesimal accretion with three models of in situ, inward migration, and reversed migration to explore terrestrial formation in tightly compact systems of M dwarfs. In the simulations, the solid discs are assumed to be 0.01 per cent of the masses of host stars and spread from 0.01 to 0.5 au with the surface density profile scaling with r−k according to the observations. Our results show that the in-situ scenario may produce 7.77+3.23 −3.77 terrestrial planets with an average mass of 1.23+4.01 −0.93 M⊕ around M dwarfs. The number of planets tends to increase as the disc slope is steeper or with a larger stellar mass. Moreover, we show that 2.55+1.45 −1.55 planets with a mass of 3.76+8.77 −3.46 M⊕ are formed in the systems via inward migration, while 2.85+1.15 −0.85 planets with 3.01+13.77 −2.71 M⊕ are yielded under reversed migration. Migration scenarios can also deliver plentiful water from the exterior of the ice line to the interior due to more efficient accretion. The simulation outcomes of the reversed migration model produce the best match with observations, being suggestive of a likely mechanism for planetary formation around M dwarfs

Speaker: Miho Tan
Affiliation: SOKENDAI (M1)
Title: Effect of stellar wind on SS433’s jet propagation
Abstract:
SS433 is an X-ray binary system consisting of a star and a compact star, and the compact star is known to emit spiral binaries. The jets propagate more than 100 pc; in Ohmura et al (2021) and other groups, uniform jets injected from 1 pc propagated 100 pc. But one of the important questions is how to travel to 1pc from the ejection region.
Therefore, in this study, we evaluate the propagation of the jet within 1pc including the effect of stellar winds. Since the orbital period of the binary is shorter than the jet propagation timescale, we assume the propagation area becomes turbulence formed by the stellar wind. We put turbulent velocity fields of 0.1% and 0.01% of the jet velocity in the ambient around the jet to see the effect of the turbulence on the jet propagation.

Facilitator
-Name: Doris Arzoumanian

Comment: English

=============== February 16 Fri==============

Campus：Mitaka
Seminar：NAOJ Seminar
Regularly Scheduled/Sporadic：Regular
Date and time：February 16, 2024 16:00-17:00
Place：Zoom/Large Seminar Room (hybrid)

Speaker：Prof. Hideyuki Kobayashi
Affiliation：National Astronomical Observatory of Japan (NAOJ)
Title：Japanese VLBI development and research that I have been involved in

Abstract: Japanese VLBI development and research that I have been involved in, are reviewed. The VSOP programme, the world’s first space VLBI observation with the HALCA satellite launched in 1997, VERA which is specialized in astrometry and began construction in 2000, as well as the organisation of the East Asian VLBI observation network with the development of the domestic VLBI network are described. Expectations for the next generation of radio telescopes, the SKA, are also discussed.

Facilitator
-Name：Takashi Moriya