EK Draconis, 2022/04/10 EK Draconis, 2020/04/05 Sun(AR 12561, C5.1), 2016/7/7
Fig. 6 of this paper from Fig. 1 & 2 of Namekata et al (2022) Nat. Astron. 6, 241

HJC 2024/12/04 by Aki Takeda

0. Research background

Superflares (1033-1036 erg) can happen on Sun-like stars. Nature paper from Kepler obs.

1. Introduction

¶ Solar flares and CMEs often have severe impacts on the planetary magnetospheres and ionospheres.

¶ Recent studies have identified possible extreme solar energetic events with energies ~1034 erg in the past millennia. Strong XUV radiation and CMEs associated with flares may intimately contribute to the formation and disruption of habitable worlds.

¶ Observations of the young solar-type stars in various phases of evolution will provide insights into the time history of our Sun and its heliosphere.

¶ Recent observations of superflares on young solar-type stars indicate stellar CMEs. To study them, time-resolved optical spectroscopic observations are currently the only approach.

Previous study: Namekata et al (2022) Nat. Astron. 6, 241


This work: Multi-wavelength observation to probe :

2. Observation and Data Reduction

2.1 EK Draconis

2.2 TESS

2.3 Seimei Telescope

2.4 NICER

Coordinated observation among 3 instruments was performed : 2022 April 10 - 21 (12 days).
Data coverage is shown in Fig.2.

3. Analysis and Results

3.1 Light Curves

Data coverage plot in Fig.2

3.2 TESS WLF Analysis

Identify significant WL enhancement in the TESS light curve, occurred simultaneously with H-alpha and X-ray flares. Obtained light curves : Fig.3(E1), Fig.4(E2) & Fig.5(E3).

Time lag of Optical and X-ray light curves : consistent with Neupert effect

Calculation of bolometric WL flare energy : assuming 10,000K black body radiation spectrum. ---> Table 2

3.3 H-alpha Flare Analysis

Time evolution of pre-flare subtracted H-alpha spectra :

Spectral fitting of the blueshifted components ---> Velocity estimate of the blueshifted component.

Light curve of EW (pre-flare state subtracted) ---> H-alpha radiated energy. (EK Dra continuum flux multiplied by the enhanced H-alpha EW and integrated in time.)

Derived parameters are listed in Table 3 and 4.

3.4 X-ray Flare Analysis

Spectral analysis of the increased intensity during the flares (for each block of data).
---> Temperatures and Emission Measures (Assuming emission spectrum from collisionally ionized diffuse gas, etc.)
---> flare radiation fluxes and energies in various energy range. "bolometric X-ray" is defined as the quantities integrated over 0.1-100 keV. Derived parameters are listed in Table 5, 6 & 7.

4. Time Evolution, Energetics, and Length Scale

4.1 Time Evolution of Optical and X-Ray Flares

4.2 Flare Radiative Energy Partition

Comparison of bolometric flare energy among WL H-alpha and X-ray

4.3. Length Scale of Flare Loop

5. Prominence Eruptions on a Young Solar-type Star

5.1. Discovery of Blueshifted Emission Spectra as Evidence of Stellar Prominence Eruptions

"we concluded that we discovered prominence eruptions on a solar-type star for the first time (undoubtedly for flare E1)."

5.2. Properties of Prominence Eruptions

5.3. Candidate of Possible X-Ray Dimming

Example of dimming after a flare.

Analysis of E1 X-ray data after the flare (block 5 and 6).

"This supports that the observed postflare decrease in soft X-ray count rate can be related to the escape of hot coronal plasma associated with a CME."

6. Discussion and Conclusion

nearly 4 pages of description ....

6.4 Future Work

Appendix

Solar CME spectral analysis. Otsu et al. (2022)