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