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2021.8.30-2021.9.5

Sep 1 Wed 15:00~16:00   ALMA-J seminar         zoom

Sep 3 Fri 13:30~15:00   Solar and Space Plasma Seminar  zoom

Sep 3 Fri 14:00~15:00   Tea Talk    zoom

Sep 3 Fri 16:00~17:00   NAOJ Seminar      zoom       

詳細は以下をご覧下さい

9月1日(水)

Campus: Mitaka
Seminar: ALMA-J seminar
Regularly Scheduled/Sporadic: Every Wednesday Date and Time: 2021 Sept 1 15:00-16:00
Place: Zoom
Speaker:Mihoko Konishi (Oita University)
Title: TBD
Abstract: TBD

Facilitator: Yoshito Shimajiri/ Shun Ishii

9月3日(金)

Campus: Mitaka
Seminar: Solar and Space Plasma Seminar
Regularly Scheduled/Sporadic: Scheduled
Date and time:3 September (Fri), 13:30-15:00
Place: zoom
Speaker:Takahiro Hasegawa
Affiliation: Tokyo University
Title:Characterization of the EUV Hydrogen Lyman Transitions in the
Solar Atmosphere

Abstract:To solve the atmospheric heating problem in the Sun, it is essential
to understand the physics and plasma conditions in the chromosphere,
the interface atmosphere of the energy source and the region where the
energy is converted into the heat, i.e., the photosphere and the
corona. However, the intermediate plasma conditions in the
chromosphere make complicated an accurate realistic modeling of its
dynamics and the radiative transfer, thus interpreting the
observations of chromospheric emission. Hence, our access to the
chromospheric spectral lines is limited. For a better understanding of
the atmospheric heating, we have to access new spectral windows that
fill the diagnostic gaps in the chromosphere.

We suggest that the hydrogen Lyman transitions, which fall in the
extreme ultraviolet (EUV) regime, are good candidates for the purpose.
On the other hand, our knowledge on the spectroscopic and formation
properties of the Lyman lines is far from satisfactory because of
limited observations of the lines and difficulties on modeling the
chromospheric spectral lines.

Motivated by the situation mentioned above, we characterize the
spectral features of the Lyman lines, in particular Lyβ, by solving
the full non-local thermal equilibrium (NLTE) radiative transfer
considering the partial redistribution (PRD) effects and numerically
modeling the Lyman spectra. We relate the response of its core, wing,
and spectral shape to the atmospheric properties in the chromosphere
and reveal how the Lyβ bridges the diagnostic gaps and how the line
contributes to solving the coronal heating problem.

After determining the best RH configuration using the FALC atmosphere,
we obtained the spatial distribution of synthetic Lyβ spectra emerging
from the 3D realistic atmospheric model computed with the BIFROST
code. We found that the core forms in the upper chromosphere of T ∼
23,000 K. The Doppler shifts found for the line core correspond to the
vertical velocity at the formation height in the model atmosphere, and
the core intensities are well correlated to the squared electron
density and the solar features’ geometry there. We concluded that the
Lyβ core is an excellent diagnostic to probe the upper chromosphere.

We took a step further, aiming to understand the relation between the
Lyβ spectral features, e.g., line asymmetries, and the atmospheric
properties, e.g. temperature or LOS velocity, in the 3D realistic
simulation. We applied a cluster analysis on the synthesized Lyβ
spectra based only on the shape of the profile, which allowed us to
determine 32 groups. We derived the relation between a typical
spectral profile and the corresponding typical stratifications of the
atmospheric parameters in each group. We discovered that we could
narrow down the obtained 32 groups to six families of profiles that
shared similar spectral features. This extra grouping helped us define
the relationship between spectral shapes and atmospheric structures,
for example, between emission peak asymmetries and chromospheric
velocity gradients. We further applied the cluster analysis on
observations of Lyβ spectra taken by the SUMER instrument on board the
SoHO spacecraft. We discovered that deeply reversed Lyβ spectra tend
to be distributed at the boundary of magnetic field concentrations, in
particular, between positive and negative magnetic patches, which is
consistent with that found in the synthesized spectra. We detected
some discrepancies between synthesized and observed spectra, though.

We conclude that the Lyman lines potentially fill the chromospheric
diagnostic gaps and help us understand the physical properties there,
which has a crucial role in heating the upper atmosphere. Space-born
EUV spectrometers in the next generation of the 2020’s, i.e., the
Solar-C (EUVST) and Solar Orbiter/SPICE, will observe some Lyman
transitions. Our achievements will be theoretical rationales to
interpret the Lyman spectra taken in the future observations.

Comment:in English,

Facilitator: Takayoshi oba

9月3日(金)

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:9/3(金)14:00~15:00
場所:Zoom
講演者:都築 寛子さん
所属:天文情報センター
タイトル:国立天文台の国際広報―海外メディアへの発信、SNS、翻訳などー

世話人:藤田登起子

9月3日(金)

Campus: Mitaka
Seminar: NAOJ Seminar
Regularly Scheduled/Sporadic: Scheduled
Date and time:3 September (Fri), 16:00-17:00
Place: zoom
Speaker:泉 拓磨 / Izumi, Takuma
Affiliation:ハワイ観測所 / Subaru Telescope
Title: すばるとALMAで挑む銀河とブラックホールの始原的共進化

Abstract:
すばる望遠鏡Hyper Suprime-Cam (HSC)は、その優れた高感度サーベイ能力で、
赤方偏移z > 6の遠方宇宙においても多数のクエーサーを発見し続けている。
クエーサーは超巨大ブラックホールの位置を示すビーコンでもあるので、
これらは近傍宇宙で知られる銀河質量とブラックホール質量の間の
強い相関関係(銀河とブラックホールの「共進化」関係として知られる)
の宇宙史的変遷を調べる格好のターゲットである。
本講演では、そのHSCクエーサーの母銀河に対する一連のALMA観測の成果を紹介する。
宇宙年齢10億歳以下の時点で存在する大質量銀河、
めくるめく星形成活動の多様性(爆発的星形成から静的状態まで)、
銀河合体現象とクエーサー活動の関連、星形成活動を阻害する中心核アウトフロー、
そして当時の宇宙の銀河 vs ブラックホール質量関係。
これらの観測結果を「共進化」の観点から読み解きつつ、
更なる研究深化を目指す我々の将来計画も紹介させて頂く。

Facilitator: Hamana, Takashi

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