カテゴリー: 科学研究部コロキウム

August　8　Tue　 10:00-11:00 　　　SOKENDAI Doctoral Thesis Preliminary　 Evaluation　　　　　　　　 Zoom / Lecture Room (hybrid)

August　9　Wed　　　15:30-16:30 　NAOJ Science Colloquium 　　

Zoom / Large Seminar Room (hybrid)　　 　　　　　　　　　　　　　　　　

詳細は下記からご覧ください。

=============== August　8　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：August 8, 2023, 10:00～11:00
Place：Lecture Room and Zoom

Speaker：Nao Fukagawa
Title：Chemical Evolution of Dwarf Galaxies

Facilitator
-Name：Hideyuki Kobayashi

:Natsuko Fujii (Graduate Student Affairs Unit)

=============== August　9　Wed===============

Campus：Mitaka
Seminar：NAOJ Science Colloquium
Regularly Scheduled/Sporadic：Every Wednesday
Date and time：2023 Aug. 9, 15:30-16:30
Place：Zoom / the large seminar room (hybrid)

Speaker：Lars Bonne
Affiliation：SOFIA Science Center, USRA, NASA Ames
Title：The assembly and dispersal of dense gas in star forming regions
Abstract：
First, I will present work analyzing multiple spectral lines toward
low- and high-mass star forming regions. The study employs archival HI
data, CO observations from the NANTEN2, APEX, and IRAM 30m
observatories, and [CII] observations with the SOFIA telescope. In these
regions we demonstrated the presence of recurring organized velocity
fields, also found by other authors, which suggests that star formation
is initiated by the same mechanism. Namely, magnetic field bending in
high-velocity (>7 km/s) colliding flows. This appears to be consistent
with magnetic field observations in several nearby clouds, which
suggests that the proposed scenario might be widespread and explain both
low- and high-mass star formation.
In the second part, I will present observations of the [CII] spectral
line by the FEEDBACK legacy program toward ~10 ionized (HII) regions
surrounding massive O stars. [CII] is the main coolant of the neutral
ISM in photodissociation regions (PDRs) and thus an excellent probe to
study the effect of stellar feedback on the host molecular cloud. The
[CII] emission reveals previously undetected high-velocity gas (10-20
km/s) in all regions. This high-velocity gas is the result of expanding
bubbles and continuous mass ejection in flattened molecular clouds. The
detection of this high-velocity gas has reignited the discussion whether
radiation or stellar winds drive molecular dispersal. Quantifying the
mass ejection rates also allows us to make a direct estimate of
molecular cloud dispersal timescales which consistently points to a few
(< 5) Myr. This provides direct observational evidence that molecular
cloud are transient structures and not in quasi-static equilibrium.

Facilitator
-Name：Doris Arzoumanian
-Comment：English

July 　19　 Wed　　　10:30-12:00 　　　　 SOKENDAI Colloquium 　　

Zoom / the large seminar room (hybrid)

July 　19　Wed　 　 13:30-14:30　　　　 　NAOJ Seminar

Zoom / the large seminar room (hybrid)

July　19 　Wed　　15:30-16:30 　　　　NAOJ Science Colloquium 　

Zoom / the large seminar room (hybrid)

詳細は下記からご覧ください。

=============== July 　19　Wed===============

Campus：Mitaka
Seminar：SOKENDAI Colloquium
Regularly Scheduled/Sporadic：Regular
Date and time：July 19, 2023 10:30-12:00
Place：Large Seminar Room in Subaru Building and Zoom

Speaker: Miho Tan
Affiliation: SOKENDAI 1st year (M1) (Supervisor: Mami Machida, Tomoya Takiwaki, Kazunari Iwasaki)
Title: The history of mass ratio determination of X-Ray Binary SS433

Speaker : Kousuke Ishihara
Affiliation: SOKENDAI 4th year (D2) (Supervisor: Masao Saito, Fumitaka Nakamura, Patricio Sanhueza)
Title: Observational study of the fragmentation process in nearby star-forming regions

Facilitator
-Name：Matsuda, Graduate Student Affairs Unit

=============== July 　19　Wed===============

Campus：Mitaka
Seminar：NAOJ Seminar
Regularly Scheduled/Sporadic：Spordiac
Date and time：2023 July 19, 13:30-14:30
Place：Zoom / the large seminar room (hybrid)

Speaker：Prof. Dr.Reinhard Genzel
Affiliation：Max-Planck Institute for Extraterrestrial Physics, Garching, Germany
Title：Testing the Massive Black Hole Paradigm in the Galactic Center
Abstract：
The discovery of the Quasars in the 1960s led to the ‘massive black hole paradigm’ in which most galaxies host massive black holes of masses
between millions to billions of solar masses at their nuclei, which can become active galactic nuclei
and quasars when they accrete gas and stars rapidly. I will discuss the major progress that has happened
in the last decades to prove the massive black hole paradigm through ever more detailed, high resolution observations,
in the center of our own Galaxy, as well as in external galaxies and even in distant quasars.
In the Galactic Center such high resolution observations can also be used to test General Relativity in the regime of large masses and curvatures.

Facilitator
-Name：Fumitaka Nakamura

=============== July 　19　Wed===============

Campus：Mitaka
Seminar：NAOJ Science Colloquium
Regularly Scheduled/Sporadic：Every Wednesday
Date and time：2023 July 19, 15:30-16:30
Place：Zoom / the large seminar room (hybrid)

Speaker：Masato Sato
Affiliation：NAOJ (D2)
Title：Light curves of electron capture and Fe core collapse supernovae:
The diagnostic method of electron capture supernovae
Abstract：
While massive stars (M>~10Msun) explode as Fe core collapse supernovae
(FeCCSNe) at their last moment, those have slightly lower mass
(M~8-10Msun) are theoretically expected to form O+Ne+Mg degenerated
core, become Super Asymptotic Giant Branches (SAGB) and finally explode
as electron capture supernovae (ECSNe) if their envelope is remained
(Miyaji et al. 1980; Nomoto et al. 1982; Nomoto 1984, 1987). However,
such evolutionary path and the mass boundary between FeCCSN and ECSN are
not confirmed and constrained by observation because of insufficient
observations of ECSNe. The reasons why we could hardly diagnose ECSN
clearly are that observational characteristics of ECSNe comparing to
low-mass FeCCSNe are not understood sufficiently, and the diagnostic
method of ECSNe is not established yet. Although Kozyreva et al. (2021)
shows that ECSN has blue plateau, they don’t include circumstellar
material (CSM) interaction. However, CSM interaction might change the
light curve significantly (Moriya et al. 2018). Thus, we synthesized the
multicolor light curves of ECSNe and low-mass FeCCSNe including CSM
interaction using the multi-group radiation hydrodynamics code, STELLA
(Blinnikov et al. 1993). As a result, ECSN is revealed to show bluer
plateau than low-mass FeCCSN even if it has reasonably dense CSM. Using
this characteristic, we propose the first diagnostic method of ECSN in
which the transition time from plateau to tail phase (tPT) and the color
index B-V at tPT/2 are used. In the talk, we will show the calculated
light curves of ECSN and low-mass FeCCSN and discuss their
characteristics. In addition, we will propose the diagnostic method of
ECSN. Also, we will mention our future work in which we will try to find
an ECSN and reveal its nature.

Speaker：Kaho Morii
Affiliation：NAOJ (D2)
Title：Early Fragmentation in Infrared Dark Clouds
Abstract：
The study of infrared dark clouds (IRDCs) sheds light on the initial
conditions governing the formation of high-mass stars and stellar
clusters. We have conducted high-angular resolution and high-sensitivity
observations toward thirty-nine massive IRDC clumps, mosaicked by the
Atacama Large Millimeter/submillimeter Array. These clumps,
characterized by their darkness at 70 μm, as well as their density and
low temperature, are thought to be the ideal sites as the birthplace of
high-mass stars. We succeeded in identifying an unprecedented number of
839 cores, with masses between 0.05 and 81 Msun. With this large sample,
we investigated the fragmentation properties in the very early stage of
high-mass star formation. By employing the minimum spanning tree method,
we calculated core separations ranging from 0.1 pc to 0.4 pc. To discern
the dominant mechanism behind early fragmentation, as well as the
hierarchical nature of the process, we compared these observed core
separations and masses with those expected from Jeans length and masses,
respectively. Our analysis implies that thermal Jeans fragmentation of
clumps is the dominant mechanism deriving the observed properties
especially for the formation of gravitationally bound cores.
Additionally, we find that some clumps exhibit a wide dynamic range of
core masses, spanning from low to high masses while others show a
narrower range. Clumps with a higher protostellar core fraction tend to
display a wider range. Furthermore, our sample highlights the complex
nature of fragmentation, characterized by various patterns such as
aligned, spread, and concentrated distributions. These findings provide
valuable insights into the mechanisms deriving high-mass star formation.

Facilitator
-Name：Haruka Kusakabe
-Comment：English

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

July 　12　Wed　 　 10:00-12:00　　　　SOKENDAI Colloquium 　　

Zoom / the large seminar room (hybrid)

July　12 　Wed　　15:30-16:30 　　　　NAOJ Science Colloquium 　

Zoom / the large seminar room (hybrid)

詳細は下記からご覧ください。

=============== July 　11　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：7月11日（火曜日）10時00分～11時30分
場所：zoom
講演者：西田信幸

世話人の連絡先
　名前：渡部潤一

=============== July 12 Wed ===============

Campus：Mitaka
Seminar：SOKENDAI Colloquium
Regularly Scheduled/Sporadic：Regular
Date and time：July 12, 2023 10:00-12:00
Place：Large Seminar Room in Subaru Building and Zoom

Speaker: Seiya Imai
Affiliation: SOKENDAI 1st year (M1) (Supervisor: Masayuki Tanaka, Yusei Koyama, Kiyoto Yabe)
Title: Revealing chemical evolution of galaxy by extreme emission line galaxy

Speaker : Yoshiaki Sato
Affiliation: SOKENDAI 2nd year (M2) (Supervisor: Noriyuki Narukage, Takashi Sekii, Masumi Shimojo)
Title: Development and Evaluation of Pre-collimator for FOXSI-4 Sounding Rocket Experiment

Speaker: Suzuka Nakano
Affiliation: SOKENDAI 5th year (D3) (Supervisor: Kouichiro Nakanishi, Takashi Sekii, Takuma Izumi)
Title: Mm/submm Energy Diagnostics & Non-LTE Modeling of the AGN-Starburst Composite Galaxy NGC 7469 with ALMA

Facilitator
-Name：Matsuda, Graduate Student Affairs Unit

=============== July 12 Wed ===============

Campus：Mitaka
Seminar：NAOJ Science Colloquium
Regularly Scheduled/Sporadic：Every Wednesday
Date and time：2023 July 12, 15:30-16:30
Place：Zoom / the large seminar room (hybrid)

Speaker：Shubham Bhardwaj
Affiliation：NAOJ (D2)
Title：GRB Optical and X-ray Plateau Properties Classifier Using
Unsupervised Machine Learning
Abstract：
The division of Gamma-ray bursts (GRBs) into different classes, other
than the “short” and “long”, has been an active field of research. We
investigate whether GRBs can be classified based on a broader set of
parameters, including prompt and plateau emission ones. Observational
evidence suggests the existence of more GRB sub-classes, but results so
far are either conflicting or not statistically significant. The novelty
here is producing a machine-learning-based classification of GRBs using
their observed X-rays and optical properties. We used two data samples:
the first, composed of 203 GRBs, is from the Neil Gehrels Swift
Observatory (Swift/XRT, (Gehrels et al. 2004; Burrows et al. 2005)), and
the latter, composed of 134 GRBs, is from the ground-based Telescopes
and Swift/UVOT (Roming et al. 2005). Both samples possess the plateau
emission (a flat part of the light curve happening after the prompt
emission, the main GRB event). We have applied Gaussian Mixture Model
(GMM) to explore multiple parameter spaces and sub-class combinations to
reveal if there is a match between the current observational sub-classes
and the statistical classification. With these samples and algorithm, we
spot a few micro-trends in certain cases, but we cannot conclude that
any clear trend exists in classifying GRBs. These microtrends could
point towards a deeper understanding of the physical meaning of these
classes (e.g., a different environment of the same progenitor or
different progenitors). However, a larger sample and different
algorithms could achieve such goals. Thus, this methodology can lead to
deeper insights in the future.

Speaker：Kiyoaki Doi
Affiliation：NAOJ (D2)
Title：Constraints on the dust size distributions in the HD 163296 disk
from the difference of the apparent dust ring widths between two ALMA Bands
Abstract：
The formation of planets begins with dust coagulation in
protoplanetary disks. Therefore, constraints on the dust size
distribution in the disks can be a clue for understanding planet
formation. In previous studies, the dust size has been estimated by
using the spectral index derived from multi-wavelength observations or
dust polarization observations. However, these studies provide different
results depending on their methods and models and do not reach a consensus.
In this work, we propose a new method to constrain the dust size
distribution by using the wavelength dependency of the dust ring widths.
Since larger dust grains are trapped more effectively in the gas
pressure bump, they form narrower rings. As a result, the dust rings
appear narrower at longer wavelength observations since observations are
sensitive to the dust grains whose size is comparable to the observed
wavelength.
We constrain the dust size distribution in the HD 163296 disk using
ALMA high-resolution observations in Band 6 (1.25 mm) and Band 4 (2.14
mm). We focus on the two clear dust rings in the disk and find that the
outer ring at 100 au appears narrower at the longer wavelength, while
the inner ring at 67 au appears similar between the two bands. We model
a dust ring assuming size-dependent dust trapping at a gas pressure
maxima and investigate the relation between the wavelength dependency of
the ring width and the spectral index, and the dust size distribution.
By comparing the model with the observations, we constrain the maximum
dust size a_max and the exponent of the power law dust size distribution
p. We constrain that 0.9 mm < a_max < 5 mm and p < 3.3 in the inner ring, and 35 mm < a_max > 1000 mm and 3.4 < p < 3.7 in the outer ring.
The larger maximum dust size in the outer ring suggests that the degree
of dust growth is spatially dependent, which could affect the location
of the planetesimal formation.

Facilitator
-Name：Kanji Mori
-Comment：English