カテゴリー: 国立天文台談話会

国立天文台談話会

2024.4.1-2024.4.7

April 5 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。

=============== April 5 Fri===============

Campus：Mitaka
Seminar：NAOJ Seminar
Regularly Scheduled/Sporadic：Regular
Date and time：April 5, 2024 16:00-17:00
Place：Zoom/Large Seminar Room (hybrid)

Speaker：Dr. Chervin Laporte
Affiliation：The Institute of Cosmos Science

Title：The stellar halo as a window on our Galaxy’s formation and dark matter

Abstract:The Galactic stellar halo consists of about 1-2% of the total stellar mass content of the Milky Way. Yet, it provides important clues on the formation of the Galaxy, properties of high redshift galaxies through the study of their resolved stellar populations as well as the nature of dark matter. In this talk, I will introduce the field of near-field cosmology and its goals. I will show how the Gaia mission has helped consolidate our understanding of the formation of the Milky Way but also the nature of dark matter and how numerical simulations are becoming an important tool to interpret observational data and the expected avalanche of data from upcoming spectroscopic/photometric surveys. I will then discuss some of the work we have carried out in our group on the stellar halo, covering the formation history of the Milky Way, interpretation of newly discovered substructures and the interaction of the LMC with the MW through the lens of numerical simulations.

Facilitator
-Name：Joten Okamoto

2024.3.18-2024.3.24

March 18 Mon 15:00-16:30
Solar and Space Plasma Seminar
hybrid; Insei Seminar Room in Subaru Building and Zoom

March 19 Tue 10:00-11:30
太陽系小天体セミナー
Zoom

March 22 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。

=============== March 18 Mon===============

Campus： Mitaka
Seminar： Solar and Space Plasma Seminar
Regularly Scheduled/Sporadic： Sporadic
Date and time：18 March (Mon), 15:00-16:30
Place： Insei Seminar Room and Zoom

Speaker：Mr. Takero Yoshihisa
Affiliation：Kyoto University (M2)
Title： One-dimensaional MHD simulation for prominence formation triggered by single heating event

Abstract：

I will review on the thermal non-equilibrium phenomena in the solar atmosphere, and present on my master thesis.
Plasma condensation phenomena in the corona, such as prominences and coronal rain, have been observed for many years. It is not clear whether current models can explain their formation process. In one of the proposed models that explain observational properties, the “evaporation condensation” model, a steady or quasi-steady heating at footpoints of a loop drives dense plasma evaporation into the corona and triggers the condensation.
However, it is natural to think of such steady or quasi-steady heating as the superposition of multiple heating events occurring between multiple magnetic field lines. When studying physical processes along a single magnetic field line, a single heating event should be considered as the basic unit.
We therefore investigate whether condensation occurs when the non-steady single heating event occurs at footpoints of a coronal loop. For this purpose, we set a dipped loop and solve 1.5-dimensional (one-dimensional three-vector components) magnetohydrodynamic equations, including radiative cooling, thermal conduction, gravity, and phenomenological turbulence heating. After reproducing the corona by energy input from imposed velocity perturbation at the footpoints, prominence formation is investigated by adding artificial transient localized heating. It is found that required amount of the heating per unit of time is ∼ 10^3 times larger than in steady cases. The amount of energy reaches nanoflare class. We also perform a parameter survey varying the magnitude of the localized heating rate to investigate the conditions for condensation by transient localized heating. The results show that with sufficiently strong heating, sufficient plasma is supplied to the corona to allow cooling to proceed and condensation to occur. It is essential that the loop temperature decreases and thermal conduction becomes inefficient with respect to cooling. Using the loop length L and the Field length λF, the condition for condensation is expressed as λF ≲L/2 under conditions where cooling exceeds heating.

Facilitator
-Name：Akiko Tei

Comment：Japanese (Slides will be in English)

=============== March 19 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：3月19日（火曜日）10時00分～11時30分
場所：zoom
講演者：大坪貴文

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

=============== March 22 Fri==============

Campus：Mitaka
Seminar：NAOJ Seminar
Regularly Scheduled/Sporadic：Regular
Date and time：March 22, 2024 16:00-17:00
Place：Zoom/Large Seminar Room (hybrid)

Speaker：Director General, Dr. Saku Tsuneta
Affiliation：National Astronomical Observatory of Japan

Title：素晴らしく面白かった太陽の研究
＝40年の研究生活を振り返って＝

Abstract: これまで約40年近く、大学院生や仲間の研究者の方々と、「ひのとり」の硬Ｘ線望遠鏡、「ようこう」の軟Ｘ線望遠鏡、「ひので」の可視光望遠鏡といった飛び道具に載せる望遠鏡の開発を行ってきました。翔体実験装置の開発をするには、教科書を読むだけでは不十分で、観測装置の構想から設計、製作、試験、打上げ前不具合の徹底追及、そして打上げ、飛翔結果を解析して初めて一人前になれます。衛星実験では規模が大きく開発期間も長いため、この過程を経験することが難しく、衛星実験の合間にロケット実験や気球実験も行ってきました。
談話会では、プロジェクトの立ち上げ方や進め方について自分の経験をもとに論じるのと同時に、国立天文台での6年間について所感を述べたいと思います。

Facilitator
-Name：Fumitaka Nakamura

2024.3.11-2024.3.17

March 15 Fri 14:00-15:00
Tea Talk
hybrid; Rinkoh Seminar Room and Zoom

March 15 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。

=============== March 15 Fri ===============

キャンパス：三鷹　野辺山 水沢 岡山 ハワイ
セミナー名：Tea Talk
定例・臨時の別：臨時
日時：3/15（金）14：00～15：00
場所：Zoom＋輪講室（ハイブリッド）
講演者：林　左絵子さん
所属： TMTプロジェクト
タイトル： エイリアンとのふれあいのススメ
言語：日本語

世話人の連絡先：
-名前：藤田登起子

備考：
参加方法：Zoom

=============== March 15 Fri ===============

Campus：Mitaka
Seminar：NAOJ Seminar
Regularly Scheduled/Sporadic：Regular
Date and time：March 15, 2024 16:00-17:00
Place：Zoom/Large Seminar Room (hybrid)

Speaker：Prof. Saeko Hayashi
Affiliation: National Astronomical Observatory of Japan (NAOJ)

Title：Seeking the Starlit Sky over the Moonbow
Abstract: “When you wish upon a star” sings a coqui frog where the stars filling the sky cast your shadow on the ground. That is where the Earth astronomers gather and strive to understand those stars seen and unseen. Each one of us with different background and skillsets can make a difference when working together to enhance such endeavor. As my last “talk story” at NAOJ, I would like to look back the changes the Japanese astronomy community has made and is going through. Naturally the emphasis is in the tools of the observations where I have had a fortune of hands-on experiences. And my parting word borrowed from the same song would be “anything your heart desires will come to you,” like how the way-finders of Hawai‘i say, even if the making of the segments for TMT is still underway.

Facilitator
-Name：Fumitaka Nakamura

2024.3.4-2024.3.10

March 4 Mon 9:00-10:00
NAOJ Seminar
hybrid; Large Seminar Room in Subaru Building and Zoom

March 5 Tue 10:00-11:00
太陽系小天体セミナー
Zoom

March 5 Tue 15:00-16:00
Tea Talk
hybrid; Rinkoh Seminar Room and Zoom

March 6 Wed 14:30-15:30
ALMA-J seminar
hybrid; Room 102 in the ALMA building and Zoom

March 6 Wed 15:30-16:30
NAOJ Science Colloquium
hybrid; Large Seminar Room in Subaru Building and Zoom

March 8 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。

=============== March 4 Mon ===============

Campus：Mitaka
Seminar：NAOJ Seminar
Regularly Scheduled/Sporadic：Sporadic
Date and time：March 4, 2024 9:00-10:00
Place：Zoom/Large Seminar Room (hybrid)

Speaker：Dr.Francisco (Paco) Colomer

Affiliation：Ministerio de Ciencia, Innovación y Universidades

Title：A voyage of discovery

Abstract: Along the last 30 years, I have been involved in many projects at
national, European and global levels. A personal voyage of discovery,
from my PhD on VLBI observations of maser emission, to the construction
of a 40-m radio telescope in Yebes, the direction of JIVE as central hub
of the European VLBI Network, to the set up of a Global VLBI Alliance.
Now back in Spain, taking care of European policy and research
infrastructures, at the Ministry of Science, Innovation and
Universities. All of it with a common background: love for knowledge and
international collaboration.

Facilitator
-Name：Fumitaka Nakamura

=============== March 5 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：3月5日（火曜日）10時00分～11時30分
場所：zoom
講演者：長谷川均

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

=============== March 5 Tue===============

キャンパス：三鷹　野辺山 水沢 岡山 ハワイ
セミナー名：Tea Talk
定例・臨時の別：臨時
日時：3/5（火）15：00～16：00
場所：Zoom＋輪講室
講演者：林　左絵子さん
所属： TMTプロジェクト
タイトル： 宇宙とのふれあいのススメを推める
言語：日本語

世話人の連絡先：
-名前：藤田登起子

備考：
参加方法：Zoom

=============== March 6 Wed==============

Campus: Mitaka
Seminar: ALMA-J seminar
Date and time: March 6 (Wed) 14:30-15:30
Place: hybrid (room 102 in the ALMA building and Zoom)

Speaker: Ikki Mitsuhashi
Affiliation: Tokyo University/ NAOJ
Title: Dust-obscured star formation of the UV-selected galaxies at high-z

Abstract:
Abstract: We present the recent study about the dust continuum emissions of UV-selected star-forming galaxies at z~5 and z~6. The datasets are mainly composed of two ALMA programs, the ALMA Cycle 8 large program CRISTAL for z~5 and the multi-band observation program SERENADE for z~6. By utilizing the combination of the identification of high-z galaxies with optical telescopes and the follow-up observations with the Atacama Large Millimeter/submillimeter Array (ALMA), we measured the statistical properties of the spectroscopically-confirmed galaxies at z=4-6.5. We constrained the obscured fraction of the star formation (fobs), defined as SFR[IR]/SFR[UV+IR], spatial extent of the dust continuum, IR luminosities, the dust temperature, and the dust-obscured star formation rate density. Our constraints on Mstar-fobs relation support that the obscured fraction at the range of Mstar<10^10Msun does not show clear evolution from z=0-2.5, but may decrease at the range of Mstar>10^10Msun. For an individual view, the spread from an average Mstar-fobs relation (Δfobs) shows a possible correlation with the compactness of SF region and the spatial offset between UV and dust continuum at z~5. Typical dust continuum sizes are ~1.5 kpc, and appear to be about two times more extended than the UV continuum. Our results show a lower IRX value by ~1 dex at βUV~0, and support the shallow IRX-βUV relation suggesting a good agreement with the metal-poor nature of the high-z galaxies. Estimated redshift evolution of Tdust with the combination of the analytical models and some observational constraints on the metallicity (Z) and gas depletion timescale (tgas) indicates the gentle increase of Tdust at high-z is naturally explained by an ~0.6 dex increase in tgas and ~0.4 dex decrease of Z. The dust-obscured star formation exhibits 40-150% star formation in the bright-UV galaxies (MUV<-20 mag) compared with the dust-unobscured star formation at z=5-6. The dust-obscured star formation may have an important role owing to their contribution to total SFRD.

=============== March 6 Wed==============

Campus: Mitaka
Seminar: NAOJ Science Colloquium
Date and time: 2023 Mar. 6 (Wed.), 15:30-16:30
Place: the large seminar room / Zoom (hybrid)

Speaker: Aoto Yoshino
Affiliation: The University of Tokyo (M1)
Title: Formation of streamers by dense core collisions
Abstract:
Stars are formed by the gravitational contraction of dense cores in molecular clouds. In the classical model, a nearly axisymmetric core gravitationally collapses to form a disk around the protostar (e.g., Terebey et al. 1984). On the other hand, recent high-resolution observations of protostellar cores have often revealed non-axisymmetric, elongated flows of material falling into the disk, called streamers (Pineda et al. 2020; Valdivia-Mena et al. 2022). Per-emb-2 is a protostellar system located in the Perseus Molecular Cloud at 300 pc, and interferometric observations with ALMA and other instruments have revealed a large, carbon-chain molecule-rich streamer structure (Pineda et al. 2020). However, the origin of streamers is still unknown, and core collisions are one candidate. In this study, we investigate the collision process of cores using three-dimensional hydrodynamic simulations and explore the formation process of non-axisymmetric streamers that appear in the circumstellar structure.

Speaker: Hiroko Okada
Affiliation: University of Hyogo (D1)
Title: The origin of extremely metal-poor star with weak r-process signature
Abstract:
The origin of the rapid neutron-capture process is a major question in astrophysics. The clue to answer this question is the chemical abundance patterns of metal-poor stars, which are believed to reflect the nucleosynthesis yields of a single event. Recent observations propose two r-process classes: the “main r-process” for light and heavy elements and the “weak r-process” for lighter ones. Aoki et al. (2017) suggested to use abundance ratios of first-peak neutron-capture elements (Sr-Ag) in metal-poor stars to identify the origin of weak r-process nucleosynthesis. However, their sample is not necessarily extremely metal-poor, and some contamination of main r-process, and even s-process, is suspected. To clarify the weak r-process’s pure abundance pattern, we studied the extremely metal-poor star SMSS J022423.27-573705.1, with a high lower limit on [Sr/Ba] ratio (Jacobson et al., 2015). Analyzing near UV spectrum data from the VLT/UVES, we measured 26 elemental abundances including first-peak neutron-capture elements and determine Ba abundance. We also compare our results with the latest nucleosynthesis models.

Facilitator
-Name: Kazumasa Ohno

Comment: English

=============== March 8 Fri===============

Campus：Mitaka
Seminar：NAOJ Seminar
Regularly Scheduled/Sporadic：Regular
Date and time：March 8, 2024 16:00-17:00
Place：Zoom/Large Seminar Room (hybrid)

Speaker：渡邉恵理子　Eriko Watanabe

Affiliation：電気通信大学 The University of Electro-Communications(UEC)

Title：天体観測に向けた深層学習に基づく大気揺らぎ抑制シングルピクセルイメージング

Abstract: 天体観測や防災用の遠隔監視の場面において，高精度なイメージングシステムの要求は高い．しかし，これらの場面では時間的に変動する不均一な空間位相分布である大気ゆらぎの影響をうけ，光波が乱れるため，精度が低下する課題ある．
　近年，一般的な二次元撮像素子と比べ耐ノイズ性に優れるイメージング技術であるSingle-Pixel Imaging(SPI)が注目されている．SPIは，対象物体の反射光もしくは透過光と符号化パターンとの光相関信号を用いて解析的あるいは統計的に像を再構成する手法であり，微弱光でのイメージングや光検出器の帯域を選択することで可視域外でのイメージングが可能である．
我々のグループでは，SPIの再構成過程にノイズ耐性向上のDeep Neural Network(DNN)を導入することで，大気揺らぎを抑制できることをシミュレーションおよび実験により示してきた．本講演では，天体観測に向けた深層学習に基づく大気揺らぎ抑制シングルピクセルイメージングの研究開発に関して，Kolmogorov乱流理論に則った大気ゆらぎの生成と本イメージングシステムにおける耐性効果の評価，大気ゆらぎなどの実問題に応用する際の学習コスト課題を抑制するDNNの提案と評価，天体望遠鏡への搭載に向けたSPI光学実験基盤等に関して紹介する。

Facilitator
-Name：Fumitaka Nakamura

2024.2.19-2024.2.25

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