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Date	Section	Speaker	File
4/14		Asai	upload or download

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Presentation time for speaker is: 60 minutes as a guide, and 30 minuites discussion.
(A speaker can use the full time of one seminar.)
Contents of talk are: :about your study
:review of recent interesting paper and share information of recent study of the Sun.
Language of slide and talks: Master cource students : Language of slide and talk could be Japanese
Doctor cource students and over : Slide must be English, and talking language could be Japanese
(If those who could not understand Japanese attend the seminar, it is preferable that you talk in English)
Title and Abstract: Please send the title and abstract of your presentation by the day before.
Presentation files: Please upload your presentation files by the start of the seminar.
If the presentation file has very large volume, please zip the file before uploading.
If you do not want to make public your unpublished results, please delete the relevant part before submission.

For Audiences

Honoring speakers: Plase clap your hands as a closure of a presentation to express your respection to a speaker.

For everyone

Publication sharing: Please send a copy of the submitted version of any paper on which they are working to the zasshikai mailing list just after submission

Useful webpage list for solar observers.

Date		Name	Title	Abstract	File
4/14		Asai
4/21		Ueno	Multi-wavelength 2D Spectroscopy of the Solar Flare at δ-type Sunspot Region	At the ASJ Annual Meeting last month, I reported on results of the analysis of multi-wavelength spectroheliograph data (H-alpha, H-beta, H-gamma and CaII K) on the M-class flare that occurred on November 25, 2024 and a dark filament, plage around δ-type sunspot region (AR13906). However, since I couldn't make time for discussion at the ASJ meeting, I would like to introduce these analyses again in this Solar Seminar with adding some additional slides.	pdf 8.0 MB
4/28		Ishii		Today, I would like to introduce following paper, Identifying Coronal Mass Ejection Active Region Sources: An Automated Approach Julio Hernandez Camero(1), Lucie M. Green(1), and Alex Pinel Neparidze(2) (1)Mullard Space Science Laboratory, University College London, UK (2)University College London, UK ApJ, 973, 63, 2025 https://ui.adsabs.harvard.edu/abs/2025ApJ...979...63H/abstract	pptx 4.8 MB
5/12		Dai	End-view Observations of longitudinal oscillations of a quiescent prominence	Combining the Doppler velocities derived from the spectroscopic data provided by CHASE/HIS and SDO/AIA EUV data, we present the end-view Observations of longitudinal oscillations of a quiescent prominence, Based on the 3D velocity (values and directions) variations of the oscillation, we confirmed that the direction of the oscillations was longitudinal, and the geometry of the magnetic dip could be accurately described: the curvature radius of the magnetic dip was the smallest at its bottom and increased towards the sides, with a range of values of 87-258 Mm. Compared to the general pendulum model (Semicircular geometry), the calculations based on the variation of V3D are more realistic and accurate.	pdf 4.5 MB
5/19		Shirato	Report on the re-analysis of full-disk oscillation data	In addressing the chromospheric and coronal heating problem, it is essential to clarify the relationship between wave propagation in the solar atmosphere and magnetic field structures in order to understand the mechanisms of energy transport to the upper layers from the perspective of wave dynamics. In particular, in quiet-Sun regions, a key focus is how low-frequency acoustic waves propagate into the upper atmosphere and dissipate their energy. It has been proposed that when relatively strong, inclined magnetic fields are present, the acoustic cutoff frequency is reduced, allowing low-frequency waves to leak into the chromosphere (De Pontieu et al. 2004). Indeed, observational studies have reported that magnetic elements and chromospheric mottles often exhibit oscillations with periods of 5–7 minutes, whereas 3-minute oscillations are more common within the internetwork regions (Jess et al. 2023). However, most of the observational studies conducted thus far have been limited to small areas near the disk center and short time spans of only 2–3 hours at most. In this study, we analyzed over 12 hours of full-disk spectroscopic imaging data in the Hα line obtained on May 4, 2022, with the SMART/SDDI instrument at Hida Observatory, Kyoto University. We investigated the spatial distribution of oscillation power in Doppler velocity and intensity through time-series analysis. As a result, in addition to the commonly observed 3- and 5-minute chromospheric oscillations, we found the presence of oscillations with a 20-minute period across the entire solar disk. Notably, the 20-minute oscillation power showed a remarkable spatial correlation with inclined magnetic fields in quiet regions, as well as with strong magnetic field regions such as enhanced network, plage, and active regions. We also observed that the oscillation power tended to be stronger closer to the limb. Due to the short duration of past observations, there have been very few reports of such 20-minute oscillations, and their nature remains unclear. Furthermore, we focused on quiet-Sun regions to examine the center-to-limb variation of oscillation power and phase difference, and explored the relationship with network structures. In this presentation, we report these findings and discuss their implications.	pptx 63.1 MB
6/2		Otsu	Broadening of Hydrogen Balmer lines during flares ~Simple Model Using SPECTRA code~	Solar and stellar flares often exhibit line broadenings in Balmer lines such as Hα during their impulsive pahses. Such broadeningsare thought to come from chromospheric condensation, and they give infomation of elecron density of condensation region. In Suemoto&Hiei 1959, they observed a solar flare with Balmer lines from Hα (H2) to H14 and obtained Full Width at Half Maximum (FWHM). The relation between FWHM and quantum number of upper level showed 'dip' structure, which can be explained with self-absorption and Stark broadening. Moreover, this relation can be used to obtain electron density at condensation region. Recently, I have been working on reconstructing the results of Suemto&Hiei 1959 to deepen my understanding of line broadening related to self absorption and Stark effect. In today's talk, I will share some reconstructed results. I will also mention line strength ratios of Balmer lines. Suemoto&Hiei 1959: Balmer Series Lines of the Flare and its Structure - Astrophysics Data System	pdf 1.0 MB
6/9	Guest Seminar	Yamasaki	Magnetic field diagnostic of solar filaments with spectropolarimetric observations in He I 10830 Å	Solar filaments are dense cool plasma in the solar corona. They are supported in a dip of coronal magnetic field. There are two classical models of magnetic field configuration of solar filaments; one is the normal polarity model proposed by Kippenhahn & Schlueter (1957), and the other is the reverse polarity model proposed by Kuperus & Raadu (1974). These two models are identified by the tilt direction between the magnetic field of the filament and polarity inversion line (PIL). To understand the mechanism that makes filaments unstable before their eruptions and/or solar flares, it is critical to confirm the magnetic field configuration of solar filaments. Previously, we have performed the He I 10830 Å spectropolarimetric observation targeting on quiet sun filaments with the Domeless Solar Telescope (DST) at Hida Observatory. We found that the magnetic field strength was 8-35 G and majority of the magnetic field configuration was reverse polarity (Yamasaki et al. 2023). In this study, we performed the same observation but targeting on an active region filament, which appeared in AR NOAA 13092 on September 5, 2022. The observation was carried out one hour after C class flare. As a result of our analysis of full Stokes profiles, we found the followings: deviation of the filament position from the PIL of about 10000 km, magnetic field strength of the filaments of 101±33 G, and counter-streaming flow along the filament axis with about 10 km/s. By comparing the direction of the magnetic field in filaments and the global distribution of the photospheric magnetic field, we suggested that the magnetic field configuration of the filament was intermediate of the two classical models, i.e., magnetic field of the filament was almost parallel to the PIL. In our presentation, we will also discuss the interpretation of strong Zeeman-like Stokes profiles found in linear polarization, and disambiguation method in our Stokes inversion. Furthermore, we will present the DST observation plan for this year.	pdf 4.9 MB
6/16		Mishra	Magnetic topological parameters as a indicator of pre-flaring activity	The solar flares are the most violent eruption in the solar atmosphere and during its eruptions it may release enormous amounts of stored magnetic energy in the form of kinetic energy, radiations, and acceleration of the charge particles. The overall evolution of any solar flare is basically classified in three phases such as (i)Precursor phase (energy storage phase) (ii) Impulsive phase (energy release phase) (iii) Decay phase. In this talk, we focused on the precursor phase of the solar flares. Using HMI vector magnetograms, we analyzed the pre-flare magnetic evolution of ARs 13664 and 13842, focusing on winding flux, magnetic helicity, and long lived polarity inversion lines (PILs). We found that increases in winding flux and the emergence of persistent recurrence of PILs consistently preceded all major X-class flares. These results highlight the predictive value of winding flux and long-lived PILs as key topological indicators of imminent solar eruptions.	pptx 90.3 MB
6/23		Shimada	Role of turbulent shear in saturating solar dynamo	Saturation mechanism of solar dynamo is one of the biggest issues in understanding of solar cycle. Although previous simulations with relatively low Reynolds numbers suggest that suppression of the Ω-effect is the saturation mechanism, the resulting evolution of rotation rates does not agree with solar one. In this context, we analyze 3D MHD sim. with high Re to identify the most plausible saturation mechanism operating in the sun. In particular, we decompose the induction equation based on the underlying physics and examined the dependence of each term on the mean magnetic fields. Notably, our results shows that induction by turbulent shear flow contributes most significantly to induction of fields and is suppressed with increasing fields which leads to saturation. Furthermore, this suppression can be interpreted by angular momentum conservation in turbulent shear flow.	pptx 5.6 MB
6/30		Natsume	Comparison of multiple chromospheric lines for post-flare loops accompanied by a flare	Solar/stellar flares are explosive phenomena where the magnetic energy is released by magnetic reconnection and the atmospheres are brightened. While solar flares can be observed in a spatially resolved manner, stellar ones can be observed as a single point, and we can obtain spectra or light curves. To understand stellar flares through knowledge of solar physics, an analysis of spatial integration of solar observational data into data mimicking stellar observation (Sun-as-a-star analysis) has been conducted. In stellar observation, red-shifted brightening components of H-alpha (Ha) line in a flare on an M-type dwarf have been detected and the component in the late phase can be considered as postflare loops. In solar research, Sun-as-a-star analysis of postflare loops in Ha line has revealed that the brightening/darkening components from postflare loops can be detected in Sun-as-a-star data. However, physical conditions for the brightening/darkening of solar/stellar postflare loops are not well understood. There are observational researches on solar/stellar postflare loop in multiple chromospheric lines, but Sun-as-a-star analysis on this topic has not been conducted and the differences of postflare loop in multiple chromospheric lines is not well known. In order to search the difference of Sun-as-a-star spectra among multiple chromospheric lines of postflare loops, we performed Sun-as-a-star analysis of four chromospheric lines (Hα, CaK, Ca8542, He10830) for post-flare loop observed with DST and compared these lines. Brightening of post-flare loop appeared almost at the same time in 4 lines. CaK line has brightening in both wings as well as line center and long duration of EW brightening. He10830 line has darkening in line center as well as wing and EW darkening. To explain what physical effect made the brightening/darkening spectra, we are trying to reproduce the spectrum using SPECTRA 0-demensional non-LTE radiative transfer code.	pdf 3.7 MB
7/7		Yoshihisa	Observational Evidence of Cold Plasma in Current Sheets during Solar Flares	Plasmoids formed via magnetic reconnection have been identified in theoretical and numerical studies as a key factor enabling fast reconnection rates that greatly exceed those predicted by the Sweet–Parker model. High-resolution observations by the Solar Dynamics Observatory's Atmospheric Imaging Assembly (SDO/AIA) have confirmed the presence of plasmoids moving along current sheets, and detailed analyses of their dynamics and morphology have been conducted. In recent years, analytical studies incorporating radiative cooling have suggested that cooling can lead to the formation of dense, cold, and thin current sheets, which may promote fast reconnection. Numerical simulations have also reported that radiative cooling triggered by thermal instability enhances the generation of plasmoids. However, direct observational evidence confirming the presence of such cool plasma within current sheets under realistic astrophysical conditions remains scarce. In this study, we investigate the flare event of August 18, 2010, previously reported by Takasao et al. (2012), using Hα observations from the SMART telescope at Hida Observatory and the Sartorius telescope at Kwasan Observatory, in addition to data from the 1600 Å and 1700 Å channels of SDO/AIA. Our aim is to detect the possible presence of cool plasma within the current sheet. As a result, we identified cool plasma descending roughly in temporal and spatial synchronization with the plasmoids previously reported. Furthermore, the time difference between the appearance of the hot (193 Å) and cool (Hα) components of the plasmoids was on the order of AIA's temporal resolution (12 seconds), which is much shorter than the typical cooling timescale from coronal to chromospheric temperatures. From the observational images, we found evidence of plasma at transition region temperatures flowing into the area where the current sheet is expected to be located, suggesting that such inflows may contribute to the rapid cooling. In this presentation, we will discuss these observational results in detail and examine the origin of cold plasma in the current sheet.	pdf 5.6 MB
7/14		Ichihara	Time evolution of white-light flare accompanied by probable postflare loops on M-type dwarf EV Lacertae	White-light flares are explosive phenomena accompanied by brightening of continuum from near-ultraviolet to optical, which occur on the Sun and stars. In order to investigate the mechanism of white-light flares, we carried out simultaneous optical photometry (TESS: 6000-10000 Å) and spectroscopy (Seimei Telescope : 4100-8900 Å) of the active flaring M-dwarf EV Lacertae on 2019 September 14. We detected a flare with high-time-cadence (~ 50 sec) spectroscopic observation. At the peak, the continuum of the flare component is well fitted by a blackbody spectrum with temperature of T = 8122 ± 273 K, which is comparable with the results of previous studies . We also estimated the time evolution of the flare temperature during the decay phase, which has not been reported with high-time-cadence spectroscopy. The radiative energy of this flare within the optical range is 4.4 × 10^{32} erg, taking into account the time-dependent variation in the decreasing flare temperature and expanding flare area. Furthermore, we detected a delayed increase in the flux of Hα after the photometric flare peak, secondary increase, and gradual increase even after the white-light flare ended. Comparison of our results with light curves obtained by the Sun-as-a-star analysis of solar flares(Otsu+ 2024) indicates that these signals may be due to postflare loops near the stellar limb. Today, I will talk about detail of this event and recent analysis results.	pdf 4.4 MB

Date

Name

Title

Abstract

File

4/14

Asai

4/21

Ueno

Multi-wavelength 2D Spectroscopy of the Solar Flare at δ-type Sunspot Region

At the ASJ Annual Meeting last month, I reported on results of the analysis of multi-wavelength spectroheliograph data (H-alpha, H-beta, H-gamma and CaII K) on the M-class flare that occurred on November 25, 2024 and a dark filament, plage around δ-type sunspot region (AR13906). However, since I couldn't make time for discussion at the ASJ meeting, I would like to introduce these analyses again in this Solar Seminar with adding some additional slides.

pdf
8.0 MB

4/28

Ishii

Today, I would like to introduce following paper,

Identifying Coronal Mass Ejection Active Region Sources: An Automated Approach
Julio Hernandez Camero(1), Lucie M. Green(1), and Alex Pinel Neparidze(2)
(1)Mullard Space Science Laboratory, University College London, UK
(2)University College London, UK
ApJ, 973, 63, 2025
https://ui.adsabs.harvard.edu/abs/2025ApJ...979...63H/abstract

pptx
4.8 MB

5/12

Dai

End-view Observations of longitudinal oscillations of a quiescent prominence

Combining the Doppler velocities derived from the spectroscopic data provided by CHASE/HIS and SDO/AIA EUV data, we present the end-view Observations of longitudinal oscillations of a quiescent prominence, Based on the 3D velocity (values and directions) variations of the oscillation, we confirmed that the direction of the oscillations was longitudinal, and the geometry of the magnetic dip could be accurately described: the curvature radius of the magnetic dip was the smallest at its bottom and increased towards the sides, with a range of values of 87-258 Mm. Compared to the general pendulum model (Semicircular geometry), the calculations based on the variation of V3D are more realistic and accurate.

pdf
4.5 MB

5/19

Shirato

Report on the re-analysis of full-disk oscillation data

In addressing the chromospheric and coronal heating problem, it is essential to clarify the relationship between wave propagation in the solar atmosphere and magnetic field structures in order to understand the mechanisms of energy transport to the upper layers from the perspective of wave dynamics. In particular, in quiet-Sun regions, a key focus is how low-frequency acoustic waves propagate into the upper atmosphere and dissipate their energy. It has been proposed that when relatively strong, inclined magnetic fields are present, the acoustic cutoff frequency is reduced, allowing low-frequency waves to leak into the chromosphere (De Pontieu et al. 2004). Indeed, observational studies have reported that magnetic elements and chromospheric mottles often exhibit oscillations with periods of 5–7 minutes, whereas 3-minute oscillations are more common within the internetwork regions (Jess et al. 2023). However, most of the observational studies conducted thus far have been limited to small areas near the disk center and short time spans of only 2–3 hours at most.
In this study, we analyzed over 12 hours of full-disk spectroscopic imaging data in the Hα line obtained on May 4, 2022, with the SMART/SDDI instrument at Hida Observatory, Kyoto University. We investigated the spatial distribution of oscillation power in Doppler velocity and intensity through time-series analysis. As a result, in addition to the commonly observed 3- and 5-minute chromospheric oscillations, we found the presence of oscillations with a 20-minute period across the entire solar disk. Notably, the 20-minute oscillation power showed a remarkable spatial correlation with inclined magnetic fields in quiet regions, as well as with strong magnetic field regions such as enhanced network, plage, and active regions. We also observed that the oscillation power tended to be stronger closer to the limb. Due to the short duration of past observations, there have been very few reports of such 20-minute oscillations, and their nature remains unclear. Furthermore, we focused on quiet-Sun regions to examine the center-to-limb variation of oscillation power and phase difference, and explored the relationship with network structures. In this presentation, we report these findings and discuss their implications.

pptx
63.1 MB

6/2

Otsu

Broadening of Hydrogen Balmer lines during flares ~Simple Model Using SPECTRA code~

Solar and stellar flares often exhibit line broadenings in Balmer lines such as Hα during their impulsive pahses. Such broadeningsare thought to come from chromospheric condensation, and they give infomation of elecron density of condensation region. In Suemoto&Hiei 1959, they observed a solar flare with Balmer lines from Hα (H2) to H14 and obtained Full Width at Half Maximum (FWHM). The relation between FWHM and quantum number of upper level showed 'dip' structure, which can be explained with self-absorption and Stark broadening. Moreover, this relation can be used to obtain electron density at condensation region.
Recently, I have been working on reconstructing the results of Suemto&Hiei 1959 to deepen my understanding of line broadening related to self absorption and Stark effect. In today's talk, I will share some reconstructed results. I will also mention line strength ratios of Balmer lines.

Suemoto&Hiei 1959:
Balmer Series Lines of the Flare and its Structure - Astrophysics Data System

pdf
1.0 MB

6/9

Guest Seminar

Yamasaki

Magnetic field diagnostic of solar filaments with spectropolarimetric observations in He I 10830 Å

Solar filaments are dense cool plasma in the solar corona. They are supported in a dip of coronal magnetic field. There are two classical models of magnetic field configuration of solar filaments; one is the normal polarity model proposed by Kippenhahn & Schlueter (1957), and the other is the reverse polarity model proposed by Kuperus & Raadu (1974). These two models are identified by the tilt direction between the magnetic field of the filament and polarity inversion line (PIL). To understand the mechanism that makes filaments unstable before their eruptions and/or solar flares, it is critical to confirm the magnetic field configuration of solar filaments. Previously, we have performed the He I 10830 Å spectropolarimetric observation targeting on quiet sun filaments with the Domeless Solar Telescope (DST) at Hida Observatory. We found that the magnetic field strength was 8-35 G and majority of the magnetic field configuration was reverse polarity (Yamasaki et al. 2023). In this study, we performed the same observation but targeting on an active region filament, which appeared in AR NOAA 13092 on September 5, 2022. The observation was carried out one hour after C class flare. As a result of our analysis of full Stokes profiles, we found the followings: deviation of the filament position from the PIL of about 10000 km, magnetic field strength of the filaments of 101±33 G, and counter-streaming flow along the filament axis with about 10 km/s. By comparing the direction of the magnetic field in filaments and the global distribution of the photospheric magnetic field, we suggested that the magnetic field configuration of the filament was intermediate of the two classical models, i.e., magnetic field of the filament was almost parallel to the PIL. In our presentation, we will also discuss the interpretation of strong Zeeman-like Stokes profiles found in linear polarization, and disambiguation method in our Stokes inversion. Furthermore, we will present the DST observation plan for this year.

pdf
4.9 MB

6/16

Mishra

Magnetic topological parameters as a indicator of pre-flaring activity

The solar flares are the most violent eruption in the solar atmosphere and during its eruptions it may release enormous amounts of stored magnetic energy in the form of kinetic energy, radiations, and acceleration of the charge particles. The overall evolution of any solar flare is basically classified in three phases such as (i)Precursor phase (energy storage phase) (ii) Impulsive phase (energy release phase) (iii) Decay phase.
In this talk, we focused on the precursor phase of the solar flares. Using HMI vector magnetograms, we analyzed the pre-flare magnetic evolution of ARs 13664 and 13842, focusing on winding flux, magnetic helicity, and long lived polarity inversion lines (PILs). We found that increases in winding flux and the emergence of persistent recurrence of PILs consistently preceded all major X-class flares. These results highlight the predictive value of winding flux and long-lived PILs as key topological indicators of imminent solar eruptions.

pptx
90.3 MB

6/23

Shimada

Role of turbulent shear in saturating solar dynamo

Saturation mechanism of solar dynamo is one of the biggest issues in understanding of solar cycle. Although previous simulations with relatively low Reynolds numbers suggest that suppression of the Ω-effect is the saturation mechanism, the resulting evolution of rotation rates does not agree with solar one. In this context, we analyze 3D MHD sim. with high Re to identify the most plausible saturation mechanism operating in the sun. In particular, we decompose the induction equation based on the underlying physics and examined the dependence of each term on the mean magnetic fields. Notably, our results shows that induction by turbulent shear flow contributes most significantly to induction of fields and is suppressed with increasing fields which leads to saturation. Furthermore, this suppression can be interpreted by angular momentum conservation in turbulent shear flow.

pptx
5.6 MB

6/30

Natsume

Comparison of multiple chromospheric lines for post-flare loops accompanied by a flare

Solar/stellar flares are explosive phenomena where the magnetic energy is released by magnetic reconnection and the atmospheres are brightened. While solar flares can be observed in a spatially resolved manner, stellar ones can be observed as a single point, and we can obtain spectra or light curves. To understand stellar flares through knowledge of solar physics, an analysis of spatial integration of solar observational data into data mimicking stellar observation (Sun-as-a-star analysis) has been conducted. In stellar observation, red-shifted brightening components of H-alpha (Ha) line in a flare on an M-type dwarf have been detected and the component in the late phase can be considered as postflare loops. In solar research, Sun-as-a-star analysis of postflare loops in Ha line has revealed that the brightening/darkening components from postflare loops can be detected in Sun-as-a-star data. However, physical conditions for the brightening/darkening of solar/stellar postflare loops are not well understood. There are observational researches on solar/stellar postflare loop in multiple chromospheric lines, but Sun-as-a-star analysis on this topic has not been conducted and the differences of postflare loop in multiple chromospheric lines is not well known.
In order to search the difference of Sun-as-a-star spectra among multiple chromospheric lines of postflare loops, we performed Sun-as-a-star analysis of four chromospheric lines (Hα, CaK, Ca8542, He10830) for post-flare loop observed with DST and compared these lines. Brightening of post-flare loop appeared almost at the same time in 4 lines. CaK line has brightening in both wings as well as line center and long duration of EW brightening. He10830 line has darkening in line center as well as wing and EW darkening. To explain what physical effect made the brightening/darkening spectra, we are trying to reproduce the spectrum using SPECTRA 0-demensional non-LTE radiative transfer code.

pdf
3.7 MB

7/7

Yoshihisa

Observational Evidence of Cold Plasma in Current Sheets during Solar Flares

Plasmoids formed via magnetic reconnection have been identified in theoretical and numerical studies as a key factor enabling fast reconnection rates that greatly exceed those predicted by the Sweet–Parker model. High-resolution observations by the Solar Dynamics Observatory's Atmospheric Imaging Assembly (SDO/AIA) have confirmed the presence of plasmoids moving along current sheets, and detailed analyses of their dynamics and morphology have been conducted.
In recent years, analytical studies incorporating radiative cooling have suggested that cooling can lead to the formation of dense, cold, and thin current sheets, which may promote fast reconnection. Numerical simulations have also reported that radiative cooling triggered by thermal instability enhances the generation of plasmoids. However, direct observational evidence confirming the presence of such cool plasma within current sheets under realistic astrophysical conditions remains scarce.
In this study, we investigate the flare event of August 18, 2010, previously reported by Takasao et al. (2012), using Hα observations from the SMART telescope at Hida Observatory and the Sartorius telescope at Kwasan Observatory, in addition to data from the 1600 Å and 1700 Å channels of SDO/AIA. Our aim is to detect the possible presence of cool plasma within the current sheet.
As a result, we identified cool plasma descending roughly in temporal and spatial synchronization with the plasmoids previously reported. Furthermore, the time difference between the appearance of the hot (193 Å) and cool (Hα) components of the plasmoids was on the order of AIA's temporal resolution (12 seconds), which is much shorter than the typical cooling timescale from coronal to chromospheric temperatures. From the observational images, we found evidence of plasma at transition region temperatures flowing into the area where the current sheet is expected to be located, suggesting that such inflows may contribute to the rapid cooling.
In this presentation, we will discuss these observational results in detail and examine the origin of cold plasma in the current sheet.

pdf
5.6 MB

7/14

Ichihara

Time evolution of white-light flare accompanied by probable postflare loops on M-type dwarf EV Lacertae

White-light flares are explosive phenomena accompanied by brightening of continuum from near-ultraviolet to optical, which occur on the Sun and stars. In order to investigate the mechanism of white-light flares, we carried out simultaneous optical photometry (TESS: 6000-10000 Å) and spectroscopy (Seimei Telescope : 4100-8900 Å) of the active flaring M-dwarf EV Lacertae on 2019 September 14. We detected a flare with high-time-cadence (~ 50 sec) spectroscopic observation. At the peak, the continuum of the flare component is well fitted by a blackbody spectrum with temperature of T = 8122 ± 273 K, which is comparable with the results of previous studies . We also estimated the time evolution of the flare temperature during the decay phase, which has not been reported with high-time-cadence spectroscopy. The radiative energy of this flare within the optical range is 4.4 × 10^{32} erg, taking into account the time-dependent variation in the decreasing flare temperature and expanding flare area. Furthermore, we detected a delayed increase in the flux of Hα after the photometric flare peak, secondary increase, and gradual increase even after the white-light flare ended. Comparison of our results with light curves obtained by the Sun-as-a-star analysis of solar flares(Otsu+ 2024) indicates that these signals may be due to postflare loops near the stellar limb. Today, I will talk about detail of this event and recent analysis results.

pdf
4.4 MB

Date

Name

Title

Abstract

File

10/6

Nagata

10/20

10/27

11/10

11/17

12/1

12/8

12/15

12/22

1/5

1/19

1/26