9月21日（水）10：00～12：00 総研大コロキウム 中央棟（北）1F講義室
Sep 21 wed SOKENDAI colloquium Lecture Room
9月21日（水）13：30～14：30 理論コロキウム コスモス会館会議室
Sep 21 wed DTA colloquium Conference Room, Cosmos Lodge
9月23日（金）10：30～12：00 太陽天体プラズマセミナー 院生セミナー室
Sep 23 fri Solar and Space Plasma Seminar Student Seminar Room, Subaru Bldg.
9月23日（金）11：00～12：00 臨時理論コロキウム コスモス会館会議室
Sep 23 fri DTA special colloquium Conference Room, Cosmos Lodge
9月23日（金）13：30～15：00 太陽天体プラズマセミナー 院生セミナー室
Sep 23 fri Solar and Space Plasma Seminar Student Seminar Room, Subaru Bldg.
詳細は以下をご覧下さい。
9月21日（水）
- Campus
- Mitaka
- Seminar
- SOKENDAI colloquium
- Regularly Scheduled/Sporadic
- Regular Date and time：21 September 2016, 10:00-12:00
- Place
- Lecture Room
- Speaker
- 1.Yoshiki Hatta
- Affiliation
- M1, SOKENDAI (Supervisor; Takashi Sekii)
- Title
- Asteroseismic measurement of surface-to-core rotation in a main-sequence A star, KIC11145123
- Speaker
- 2.Ko Hosokawa
- Affiliation
- M1, SOKENDAI (Supervisor; Takayuki Kotani)
- Title
- High Dispersion Spectroscope for Detecting Exoplanet Atmospheres
- Speaker
- 3.Noriharu Watanabe
- Affiliation
- M1, SOKENDAI (Supervisor; Norio Narita)
- Title
- The Research for Orbital Evolution of Various Exoplanets from Misalignment Observation
- Facilitator
- -Name：Kotomi Taniguchi
- Comment
- TV conference system is available connecting from Nobeyama, Hawaii, Mizusawa, and Okayama.
9月21日（水）
- Campus
- Mitaka
- Seminar
- DTA colloquium
- Regularly Scheduled/Sporadic
- Regularly Scheduled Date and time：21 September 2016, 13:30-14:30
- Place
- Conference Room, Cosmos Lodge
- Speaker
- Kazunori Akiyama
- Affiliation
- MIT
- Title
- Interstellar Scintillation and Radio Counterpart of the FRBs
- Abstract
- Fast radio bursts (FRBs) are one of the most intriguing sources, not only for astrophysical processes causing one of the most energetic but shortest bursts in the universe but also for their astronomical aspect of a unique probe for the intergalactic medium. Searches for counterparts of FRBs — for instance, associated aftergrows are of significant importance for their localization. Refractive Interstellar scintillation is a critical consideration for searches for identification of associated aftergrows at radio wavelengths. The tenuous ionized interstellar medium along the line of sight can introduce rapid variability of compact radio sources such as active galactic nuclei (AGNs) on timescales comparable to potential aftergrows of the FRBs. Thus, it is quite essential to distinguish between associated aftergrows and rapidly variable scintillating sources close to FRBs. We have recently demonstrated a fundamental importance of the refractive scintillation for identification of the radio counterpart in a theoretical study on the effect of scintillation of the FRB 150418 (Akiyama & Johnson 2016, ApJL) that Keane et al. 2016 have recently discovered with a promising radio counterpart at 5.5 and 7.5 GHz — a rapidly decaying source on timescales of ~ 6 days. The analytical theory of refractive scattering and our numerical simulations show that the reported observations on FRB 150418 are consistent with scintillating radio emission from the core of a radio-loud AGN having a brightness temperature of Tb ? 10^9 K, compatible with LLAGN and faint blazars. In this talk, I introduce FRBs and interstellar scintillation with our recent works on the FRB 150418. I also briefly discuss implications for future surveys of radio counterparts of compact objects such as FRBs and gravitational waves.
- Facilitator
- -Name：Tomoya Takiwaki
- Comment
- in English
9月23日（金）
- Campus
- Mitaka
- Seminar
- Solar and Space Plasma Seminar
- Regularly Scheduled/Sporadic
- Sporadic
- Date and time
- 23 September (Fri), 10:30-12:00
- Place
- Student Seminar Room, Subaru Bldg.
- Speaker
- Takafumi Sonoi
- Affiliation
- Observatoire de Paris
- Title
- Analysis of solar-like oscillation frequencies using 3D hydrodynamical models
- Abstract
- In the Sun, the 5-minute oscillations are stochastically excited by turbulent motions in the convective envelope. The same type of oscillations have been observed in the other solar-like stars, and they are called “solar-like oscillations”. This type of oscillations have been so far detected in thousands of solar-like stars thanks to massive and continuous photometry by the spacecrafts, CoRoT and Kepler. It is allowed to perform precise seismic determination of both the global stellar parameters and stellar interiors by the detection of a large number of consecutive radial orders and angular degrees.
However, uncertainties included in theoretical stellar models prevent us from making the best of the precise seismic data. In standard stellar models, the mixing-length theory is used to model convection. However, it is poor at treating near-surface turbulence, and leads to systematic errors of p-mode frequencies. Since we still do not have any definitive solutions for this problem, model frequencies of solar-like oscillations have been corrected using an empirical law based on the solar case when comparing them with observed frequencies. However, a physically-grounded method should be established.
On the other hand, 3D hydrodynamical computations limited to surface layers and short duration compared to stellar evolution timescale come to realize realistic turbulence profiles. We then construct “patched models”, which consist of inner parts constructed by a standard stellar evolution code and outer time- and horizontally averaged 3D parts to realize more realistic frequencies. In this talk, I would like to introduce our attempt of constraining the correction of standard model frequencies using the patched models and our future plans.
- Facilitator
- -Name：Shin Toriumi
- Comment
9月23日（金）
- Campus
- Mitaka
- Seminar
- DTA special colloquium （臨時理論コロキウム）
- Regularly Scheduled/Sporadic
- Sporadic
- Date and time
- 23 September 2016, 11:00-12:00
- Place
- Conference Room, Cosmos Lodge
- Speaker
- Akimasa Kataoka
- Affiliation
- Heidelberg University
- Title
- Millimeter polarization of protoplanetary disks due to dust scattering
- Abstract
- To measure if dust grains have grown to beyond millimeter sizes in protoplanetary disks, usually measurements of the spectral slope are used. However, the interpretation of millimeter spectral slopes in terms of grain size is unreliable. We have found a completely independent way to measure grain sizes in this size and wavelength regime: scattering polarization. If grains are grown to the comparable size of the wavelengths i.e., (sub)mm, dust grains scatter the thermal emission. The scattered emission is polarized by nature. The star itself is dark at millimeter wavelengths, the main source of the radiation is thermal dust emission itself. If a protoplanetary disk has a slight anisotropy such as lopsided or ring-shaped dust density distribution, the residual polarization is up to 2.5 %, which is observable with ALMA. Moreover, it explains measured polarization of emission from e.g. HL Tau. It turns out that this also allows for an independent measurement of the grain sizes; we have constrained the maximum grain sizes to be 150 μm. Also, we report our polarization observations with ALMA toward one of the brightest protoplanetary disks, which show an evidence of the self-scattering. This allows for a new probe of the grain growth in protoplanetary disks.
- Facilitator
- -Name：Tomoya Takiwaki
- Comment
- in English
9月23日（金）
- Campus
- Mitaka
- Seminar
- Solar and Space Plasma Seminar
- Regularly Scheduled/Sporadic
- Regular
- Date and time
- 23 September (Fri), 13:30-15:00
- Place
- Student Seminar Room, Subaru Bldg.
- Speaker
- Hirohisa Hara
- Affiliation
- NAOJ
- Title
- Hinode EUV Imaging Spectroscopy at the Site of Magnetic Reconnection in Solar Flares
- Abstract
-
We show a summary of achievements with the Hinode EUV Imaging Spectrometer (EIS) on the studies of magnetic reconnection in solar flares. The topics in this presentation are those that were raised as questions in the SOLAR-B proposal and what answers we obtained from EIS observations. One of the primary roles of EIS flare observations is to reveal the structures and dynamics at the site of magnetic reconnection by the EUV emission-line imaging spectroscopy. The requirements of the EIS performance for the topics are satisfied for the measurements of (1) reconnection inflow & (2) outflow speeds, and (3) the spatial identification of the so-called turbulence that appears in the flare impulsive phase. EIS has successfully observed the plasma properties of these structures from simultaneous multiple line observations with its high sensitivity and a moderate cadence. Some EIS observations have provided the 2D mapping of specific structures, such as a thin extended fast flow of more than a few hundred km/s near the reconnection site and an isolated dense blob structure with non-thermal line broadening of
100-300 km/s located above the flare loop. The examination of complicated line profile and intensity distributions across the fast flow is capable of probing the fine-scale structures in/beside the outflows and of searching for the presence of expected MHD shocks. The interpretation of these observations is examined by other observations with different energies/wavelengths and with different viewing angle.
Based on the current achievements, the topics to be explored by the coming studies from the EIS data analysis and those from the future observations are also discussed. - Facilitator
- -Name：Shin Toriumi
- Comment
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