June 7 Wed 10:30-12:00 SOKENDAI Colloquium Zoom / the large seminar room (hybrid)
June 7 Wed 11:00-12:00 Tea Talk Zoom / conference room #2 (hybrid)
June 7 Wed 13:30-15:00 Solar and Space Plasma Seminar Zoom / the Insei seminar room (hybrid)
June 7 Wed 14:30-15:30 ALMA-J seminar Zoom / ALMA building #102 (hybrid)
June 7 Wed 15:30-17:00 NAOJ Science Colloquium Zoom / the large seminar room (hybrid)
詳細は下記からご覧ください。
=============== June 7 Wed===============
Campus：Mitaka
Seminar：SOKENDAI Colloquium
Regularly Scheduled/Sporadic：Regular
Date and time：June 7, 2023 10:30-12:00
Place：Large Seminar Room in Subaru Building and Zoom
Speaker: Abdurrahman Naufal
Affiliation: SOKENDAI 3rd year (D1) (Supervisor: Yusei Koyama, Masayuki Tanaka, )
Title: Searching for quiescent galaxies in the Spiderweb protocluster with HST grism observation
Speaker : Shunsuke Sasaki
Affiliation: SOKENDAI 4th year (D2) (Supervisor: Tomoya Takiwaki, Mami Machida, Takashi Moriya)
Title: Phenomenological turbulent effect of core collapse supernova
Facilitator
-Name：Matsuda, Graduate Student Affairs Unit
=============== June 7 Wed===============
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：6/7（水）11：00～12：00
場所：Zoom、第二会議室のハイブリッド開催
講演者：縣 秀彦
所属：天文情報センター
タイトル：ゴビ砂漠におりる一粒の雨
Abstract：2009年の世界天文年2009以降、モンゴルを旅する機会にたびたび恵まれて、大自然と人の営みについて考える機会がありました。2023年5月、2回目のゴビ砂漠への旅行を含め7回、モンゴルを訪ねたことになります。
今回の旅は、昼間に砂漠に苗木を植えて、夜には満天の星を眺める・・・エコツーリズム＆アストロツーリズムの活動です。
世話人の連絡先：
-名前：藤田登起子
=============== June 7 Wed===============
Campus： Mitaka
Seminar： Solar and Space Plasma Seminar
Regularly Scheduled/Sporadic： Scheduled
Date and time：7th June (Wed), 13:30-15:00
Place： hybrid; Subaru Building / Insei Seminar Room
Speaker：Daiki Yamasaki
Affiliation：ISAS/JAXA
Title：Numerical Modeling and Observation of Magnetic Flux Rope
Abstract：Magnetic flux ropes (MFRs) are the bundle of helical magnetic field lines from in the solar corona. It is widely accepted that an eruption of MFRs drives the fast magnetic reconnection during solar flares, and MFRs are the core structure of coronal mass ejections. To understand the eruption mechanism of MFRs, we need to obtain the magnetic field configuration of MFRs. However, due to observational limitations, we cannot observe the coronal magnetic field directly. In our study, to reproduce MFRs, we extrapolate the three-dimensional coronal magnetic field by using a photospheric vector magnetic field as a bottom boundary. We investigated the formation process and eruption mechanism of MFRs in the case of large scale solar flares. As a result, regarding the formation process, we found that the reconfiguration of magnetic field structure by successive flare activities results in the suppression of MFRs (Yamasaki et al. 2021), and regarding the eruption mechanism we found that not only the torus instability but also the magnetic reconnection below MFRs accelerate the MFRs during eruptions (Yamasaki et al. 2022). In addition, we developed a near infrared spectropolarimeter at Hida Observatory, Kyoto University, and observed solar dark filaments, which are the dense plasma materials trapped on MFRs, and obtained the two-dimensional map of vector magnetic field (Yamasaki et al. 2023). In this talk, we introduce numerical and observational studies of MFRs and discuss the difference in magnetic field configuration of MFRs between the studies.
Facilitator
-Name：Takayoshi oba
Comment：in English
=============== June 7 Wed===============
Campus：Mitaka
Seminar：ALMA-J seminar
Regularly Scheduled/Sporadic： Every Wednesday
Date and time： June 7th, 2023 (Wed), 14:30 – 15:30
Place： ALMA building #102 / Zoom (hybrid)
Speaker: Satoshi Ohashi
Affiliation: NAOJ
Title: Dust enrichment and grain growth in a smooth disk around the DG Tau protostar revealed by ALMA triple bands frequency observations
Abstract: Characterizing the physical properties of dust grains in a protoplanetary disk is critical to comprehending the planet formation process. Our study presents ALMA high-resolution observations of the young protoplanetary disk around DG Tau at a 1.3 mm dust continuum. The observations, with a spatial resolution of 0.04 arcsec, or 5 au, revealed a geometrically thin and smooth disk without substantial substructures, suggesting that the disk retains the initial conditions of the planet formation. To further analyze the distributions of dust surface density, temperature, and grain size, we conducted a multi-band analysis with several dust models, incorporating ALMA archival data of the 0.87 mm and 3.1 mm dust polarization. The results showed that the Toomre Q parameter is <2 at a disk radius of 20 au, assuming a dust-to-gas mass ratio of 0.01, which means that a higher dust-to-gas mass ratio is necessary to stabilize the disk. In addition, grain sizes depend on the dust models, and were found to be less than 0.1 -1 mm in the inner region (r<20 au), while they exceeded larger than 1 mm in the outer part. Radiative transfer calculations show that the dust scale height is lower than at least one-third of the gas scale height. These distributions of dust enrichment, grain sizes, and weak turbulence strength may have significant implications for the formation of planetesimals through mechanisms such as streaming instability. We also discuss the CO snowline effect and collisional fragmentation in dust coagulation for the origin of the dust size distribution.
Facilitator: Toshiki Saito, Andrea Silva
=============== June 7 Wed===============
Campus：Mitaka
Seminar：NAOJ Science Colloquium
Regularly Scheduled/Sporadic：Every Wednesday
Date and time：2023 Jun. 7, 15:30-17:00
Place：zoom / the large seminar room (hybrid)
Speaker：Yuki Yoshida
Affiliation：NAOJ (D3)
Title：Simulating dust monomer collisions: expansion of the JKR theory
Abstract：
Dust is aggregate of monomers. Monomer is minimum building block of
dust and have sub-μm size.
Dust grows by collisional sticking, but fragmentation can occur for
large dust, and the dust growth is stopped.
Therefore investigating dust maximum size and critical velocity of
sticking is important to understand the dust growth.
Numerical simulations of aggregate collisions have investigated the
critical velocity of dust compression and disruption, and the dust size
evolution (e.g., Wada et al. 2013; Suyama et al. 2012).
They used the JKR theory to calculate the monomer interactions.
However, dust collision experiments showed that the bouncing velocity is
larger than the theoretical value (e.g., Poppe et al. 2000, Wada et al.
2008).
It is suggested that this is because the JKR theory does not consider
microscopic physics (Tanaka et al. 2015).
Therefore, we construct a new contact model by Molecular Dynamics (MD)
simulation.
First, we performed MD simulations of monomers’ head-on collisions and
investigated the coefficient of restitution, e, changing the monomer
size, impact velocity, and temperature.
We found that e decreases with decreasing monomer radius, increasing
impact velocity larger than 50 m/s and increasing temperature.
Next, we extended the contact model by adding dissipative forces to the
JKR theory to reproduce the MD results.
We found that a dissipative force model proportional to (relative
velocity)^3 and (contact radius)^3/2 can reproduce the MD results well.
However, another energy dissipation is required to reproduce the MD
simulations for high-velocity collisions.
We discuss the MD results and the new model in my presentation.
Speaker：Chanoul Seo
Affiliation：NAOJ (D3)
Title：Two affecting mechanisms on atmospheric carbon of super-Earth:
Magma versus Atmospheric escape
Abstract：
Super-Earths are the common exoplanets with a few earth radii. The
mass and radius of super-Earth correspond to the two compositions, a
thicker atmosphere with a silicate core and an H2O-rich composition.
Atmospheric characterization is expected to give some hints about their
interior.
To find some clues for the super-Earth atmosphere and its connection
to the internal structure, previous studies (e.g., Kite et al. 2020, Hu
et al. 2021, Yu et al. 2021, and Schlichting+ 2022) discussed the
effects of chemical reactions and the planet surfaces on the atmospheric
compositions of super-Earths but with assumptions such as artificial
atmospheric metallicity, exclusion of magma, or the use of only H and
O-bearing volatiles.
In this research, we highlight the magma’s effect on the other
radiatively active species, the C-bearing species with the expectation
they can be a possible probe of the exposed magma. This effect is
compared to the atmospheric escape that also affects the atmospheric
composition through selective hydrogen escape. We assume the atmospheric
composition before the reaction as the nebula gas-like composition.
We first study the atmospheric compositions of the magma-containing
super-Earths, assuming the nebula gas accretion onto the silicate core.
We focus on H, O, and C-bearing species. We find that magma can increase
the atmospheric C/H ratio by isolating the C-bearing species in the
atmosphere because of the much higher solubility of H2O to the magma
than the C-bearing species. We quantify this effect by describing the
atmospheric C/H ratio as a function of the planetary mass, radius, and
equilibrium temperature.
To discuss the energy-limited atmospheric escape, we calculate the
resultant atmospheric composition of super-Earth by the atmospheric
escape effect. Through the quantitative calculation, we show the effect
of the atmospheric escape on the atmospheric C/H ratio with specific
planetary age prior as a function of the planetary mass, radius, and
orbital radius.
Based on these results, we compare the effect of magma and the effect
of atmospheric escape depending on planetary parameters. We also discuss
the behavior of another important element (N, nitrogen) and the
influence of various mechanisms, including the convection in magma, that
affect the atmospheric C/H ratio.
Facilitator
-Name：Masamitsu Mori
-Comment：English