| Date |
|
Name |
Title |
Abstract |
File |
| 4/8 |
|
Asai |
Solar Seminar 2024 |
|
|
| 4/15 |
|
Nagata |
Near Infrared Tunable Filter for DIKIST |
|
pptx
67.3 MB
|
| 4/22 |
|
Ishii |
Filament eruptions and two ribbon flares at quiet regions |
Today, I would like to introduce the following paper and SMART/SDDI observations of filament eruptions and two ribbon flares at quiet regions.
A STUDY OF FAST FLARELESS CORONAL MASS EJECTIONS,
H. Q. Song et al, 2013, ApJ, 773, 129.
|
pptx
10.5 MB
|
| 5/13 |
|
Mishra |
Successive Emerging Flux Triggers Persistent Reconnection Jets in the Solar Atmosphere and Associated Heating |
The dynamics of the solar atmosphere, including mass and energy circulation,
coronal heating, and the initiation of eruptions both small and large, are governed by magnetic fields.
High-resolution observational techniques and computational models are essential for unraveling these intricate phenomena.
In my presentation, I will discuss how the successive emergence of magnetic flux influences various phases of jet activity
in the solar atmosphere, contributing to the heating of the solar corona.
Utilizing AIA multiwavelength imaging and SMART/SDDI spectroscopic observations,
we categorized the observation period into three phases: initial, developing, and eruptive.
The initial phase featured small-scale jets with velocities between 175-255 km/s.
The developing phase was characterized by bidirectional plasma flows within the fan plane,
while the eruptive phase saw three homologous jets within the fan-spine magnetic topology.
We examined the topological alterations caused by magnetic reconnection and its persistent role in coronal heating.
Differential Emission Measure (DEM) analysis indicated the existence of super-hot plasma, around 8-10 MK,
which led to the ejection of hot and multithermal plasma into the overlying solar corona.
|
pptx
94.2 MB
|
| 5/20 |
@ Room 328 |
Dai |
Simultaneous Horizontal and Vertical Oscillation of a Quiescent Filament Observed by CHASE and SDO |
In this study, we present the imaging and spectroscopic observations of the simultaneous horizontal and vertical
large-amplitude oscillation of a quiescent filament triggered by an extreme-ultraviolet (EUV) wave on 2022
October 2. Particularly, the filament oscillation involved winking phenomenon in H-alpha images and horizontal
motions in EUV images. Here we focus on the EUV (Moreton) wave and the filament oscillation. |
pdf
3.4 MB
|
| 6/3 |
|
Shirato |
Overview of the IHOP 0473 observation using EIS/Hinode, IRIS and DST/Hida |
Today I would like to talk about my rescent observation, through IHOPs (IRIS/Hinode Operations Plans) observation.
This is a joint observation using IRIS, Hinode and other instruments.
I conducted IHOP observation twice using Domeless Solar Telescope (DST) at Hida Observatory, on November 2023, and on April and May 2024.
In today’s talk, I will provide an overview of these observations and the progress made so far, and the future plan.
|
pdf
18.1 MB
|
| 6/10 |
|
Otsu |
Comparison of Sun-as-a-star and Spatially-resolved Velocity of Prominence Eruptions |
Solar and stellar flares are explosive phenomena in atmospheres of the sun and cool stars.
As known from imaging observations, solar flares are sometimes associated with filament/prominence eruptions which can lead to coronal mass ejections (CMEs).
Such plasma eruptions and CMEs are thought to also accompany some stellar flares and affect exoplanet environments (e.g., Airapetian+ 2020).
In stellar cases, Doppler shifted components observed in chromospheric lines such as H-alpha are often interpreted as plasma eruptions.
Although most studies reported shifted components with velocities lower than the escape velocities of stars,
some studies showed greatly high velocity components which can escape from stars and lead to CMEs (e.g., Inoue+ 2023).
Also, some studies made direct comparison of stellar shifted components and solar H-alpha data of filament/prominence eruptions using Sun-as-a-star analyses,
and confirmed their qualitative similarities (Namekata+ 2022, 2024, Leitzinger+ 2024). Thus, the existence of stellar plasma eruptions is becoming more certain.
To clarify the quantitative relations between stellar activities and exoplanet environments, it’s required to investigate detailed dynamics of stellar plasma eruptions such as kinematic and thermal evolutions.
In this study, I focused on kinematic evolution of plamsa eruptions in spatially integrated data.
In order to clarify the relation between velocity distribution in resolved data and Sun-as-a-star velocity of plasma (prominence) eruptions,
I conducted cloud model fitting for spatially resolved H-alpha data of SMART/SDDI and compare the fitting results with velocities obtained from Sun-as-a-star H-alpha spectra.
I’d like to introduce some preliminary results and future plans. |
pptx
9.9 MB
|
| 6/17 |
|
Shimada |
Mean-Field Study of Stellar Activity-Rotation Relationship |
This study explores the relationship between stellar surface magnetic fields and rotation rates.
Previous observations (e.g., Wright+ 2011, 2018) have established a connection between stellar activity and rotation rates,
with recent observations by Reiners (2022) indicating a parallel trend in surface magnetic fields.
Observations suggest an anti-correlation between the magnetic field and Ro within the moderate Ro range (0.1 $<$ Ro $<$ 1), reaching saturation at extremely low Ro.
Here, the Rossby number (Ro) is a crucial measure in assessing the impact of rotation on dynamics defined as the rotation period over convective turnover time.
While global magnetohydrodynamic (MHD) simulations, such as those by Brun+ (2022), successfully replicate the anticorrelation in moderate Ro,
the saturation phenomenon at extremely low Ro remains beyond the reach of current global simulations, and its driving mechanism remains unclear.
To elucidate the saturation of the stellar magnetic field at extremely low Ro, We perform non-kinematic mean-field dynamo simulations by extending the solar case by Rempel (2006).
Our findings reveal that the magnetic field strength is influenced by both stellar rotation rates and the assumed turbulent angular momentum (AM) transport process.
Through detailed analysis, we demonstrate that the dependence of the magnetic field on Ro is intricately determined by the balance between AM transport by turbulence and the magnetic field.
Notably, our results, in conjunction with recent insights into turbulence properties at low Ro (e.g. Kapyla 2024), align closely with observed magnetic field saturation patterns reported by Reiners (2022).
We are also going to discuss the methods to justify the assumed turbulent effects.
|
pptx
9.9 MB
|
| 6/24 |
|
Yoshihisa |
Non-thermal velocities in Corona and Coronal Rain |
The coronal heating problem of why the corona reaches a million K relative to 6000 K at the photosphere is one of the key open questions in the stellar physics.
From an observational perspective, non-thermal line broadening are observed and considered to be the indicator of heating properties.
However, previous numerical simulations have not explained this observation.
This work attempt to reproduce observed non-thermal vel. by taking into account turbulent heating.
We also investigate the non-thermal vel. in the coronal rain.
|
pptx
12.9 MB
|
| 7/1 |
|
Kida |
|
|
|
| 7/8 |
|
Natsume |
|
|
|
| 7/8 |
Guest
Seminar
15:30-17:00 |
Prof. Petr Heinzel
(Astronomical Institute, Czech Academy of Sciences
and
University of Wroclaw, Center of Excellence 'Solar and Stellar Activity')
|
Radiative transfer in solar prominences: A historical overview and current trends |
Similarly as in other branches of solar atmospheric spectroscopy,
development of the non-LTE (i.e. departures from Local Thermodynamic Equilibrium) physics and related numerical tools in 60-ties and 70-ties of the last century largely influenced also the prominence research.
First 1D prominence models have been constructed showing the critical importance of an external illumination in the relevant spectral lines and continua.
Later on the effects of 2D geometry and partial redistribution have been investigated and the modeling turned to problems of heterogeneous media,
multithread structures and finally studies of the energy balance.
In parallel, new multi-wavelength spectral data became available at higher spatial and temporal resolution.
We will review the progress from 70-ties till now and finally summarise the current modern trends in numerical non-LTE radiative-transfer modeling,
focusing on both quiescent as well as eruptive prominences. Namely the coupling of up-to-date MHD simulations with optically-thick radiative transfer will be highlighted.
|
|
| 7/22 |
|
Suzuki |
|
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|