Optical and X-ray observations of stellar flares on an active M dwarf AD Leonis with the Seimei Telescope, SCAT, NICER, and OISTER

Namekata, Kosuke; Maehara, Hiroyuki; Sasaki, R.; Kawai, H.; Notsu, Yuta; Kowalski, Adam F.; Allred, Joel C.; Iwakiri, W.; Tsuboi, Y.; Murata, Katsuhiro L.; Niwano, Masafumi; Shiraishi, K.; Adachi, R.; Iida, Katsuyoshi; Oeda, M.; Honda, Satoshi; Tozuka, Miyako; Katoh, Noriyuki; Onozato, Hiroki; Okamoto, Soshi; Isogai, Keisuke; Kimura, M.; Kojiguchi, Naoto; Wakamatsu, Yasuyuki; Tampo, Yusuke; Nogami, Daisaku; Shibata, Kazunari

doi:10.1093/pasj/psaa051

Cited by 60 publications

(80 citation statements)

References 73 publications

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“…In addition, the superflare did not show any significant line broadening synchronized (Figure 4), which is often seen in M-dwarf superflares (e.g., ∼14 Å for a 10 33 erg-class superflare in Namekata et al 2020b) with the same spectrograph KOOLS-IFU. This indicates that high energy electrons heating is not essential for this superflare on EK Dra.…”

Section: (C))mentioning

confidence: 73%

“…The exposure time was set to be 30 sec for these nights. The data reduction follows the prescription in Namekata et al (2020bNamekata et al ( , 2021 with IRAF and PyRAF packages. Only the data of particular interest are shown in Figure 2.…”

Section: 8-m Seimei Telescopementioning

confidence: 99%

“…Furthermore, the most mysterious point is that the duration of Hα and white light is approximately the same for the EK Dra superflare. In the case of solar flares (e.g., Hao et al 2017, and see Table 1) and M-dwarf flares (e.g., Hawley & Pettersen 1991;Kowalski et al 2013;Namekata et al 2020b), the white light timescale is generally several times shorter than that of Hα. For example, the ratio of Hα and white-light duration was reported as a factor of 2 in the 10 33 erg-class M-dwarf superflares by Namekata et al (2020b).…”

Section: (C))mentioning

confidence: 99%

“…In the case of solar flares (e.g., Hao et al 2017, and see Table 1) and M-dwarf flares (e.g., Hawley & Pettersen 1991;Kowalski et al 2013;Namekata et al 2020b), the white light timescale is generally several times shorter than that of Hα. For example, the ratio of Hα and white-light duration was reported as a factor of 2 in the 10 33 erg-class M-dwarf superflares by Namekata et al (2020b). Much larger difference was reported for several M-dwarf flares by Kowalski et al (2013).…”

Section: (C))mentioning

confidence: 99%

“…Optical spectroscopic observations are also essential to capture chromospheric phenomena (accompanied by UV radiation) and filament/prominence eruptions (indirect evidence of CMEs) (cf. Ichimoto & Kurokawa 1984;Kowalski et al 2013;Namekata et al 2020b;Maehara et al 2021, for solar and M-dwarf flares). Our previous study (Namekata et al 2021) reported the first detection of the optical Hα spectra of a superflare of ∼ 10 33 erg on the young solar-type star EK Dra.…”

Section: Introductionmentioning

confidence: 99%

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Discovery of a Long-Duration Superflare on a Young Solar-Type Star EK Draconis with Nearly Similar Time Evolution for H$α$ and White-Light Emissions

Namekata,

Maehara,

Honda

et al. 2022

Preprint

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Young solar-type stars are known to show frequent "superflares", which may severely influence the habitable worlds on young planets via intense radiations and coronal mass ejections. Here we report an optical spectroscopic and photometric observation of a long-duration superflare on the young solar-type star EK Draconis (50-120 Myr age) with the Seimei telescope and Transiting Exoplanet Survey Satellite (TESS ). The flare energy 2.6×10 34 erg and white-light flare duration 2.2 hr are much larger than those of the largest solar flares, and this is the largest superflare on a solar-type star ever detected by optical spectroscopy. The Hα emission profile shows no significant line asymmetry, meaning no signature of a filament eruption, unlike the only previous detection of a superflare on this star (Namekata et al. 2021, Nat.Astron). Also, it did not show significant line broadening, indicating that the non-thermal heating at the flare footpoints are not essential or that the footpoints are behind the limb. The time evolution and duration of the Hα flare are surprisingly almost the same as those of the white-light flare, which is different from general M-dwarf (super-)flares and solar flares. This unexpected time evolution may suggest that different radiation mechanisms than general solar flares are predominant, as follows: (1) radiation from (off-limb) flare loops, and (2) re-radiation via radiative backwarming, in both of which the cooling timescales of flare loops could determine the timescales of Hα and white light.

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Section: (C))mentioning

confidence: 73%

Section: 8-m Seimei Telescopementioning

confidence: 99%

Section: (C))mentioning

confidence: 99%

Section: (C))mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Discovery of a Long-Duration Superflare on a Young Solar-Type Star EK Draconis with Nearly Similar Time Evolution for H$α$ and White-Light Emissions

Namekata,

Maehara,

Honda

et al. 2022

Preprint

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Explorations of Extreme Space Weather Events from Stellar Observations and Archival Investigations

Hayakawa

Notsu

Ebihara

2023

Solar-Terrestrial Environmental Prediction

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Stellar flares

Kowalski

2024

Living Rev Sol Phys

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Magnetic storms on stars manifest as remarkable, randomly occurring changes of the luminosity over durations that are tiny in comparison to the normal evolution of stars. These stellar flares are bursts of electromagnetic radiation from X-ray to radio wavelengths, and they occur on most stars with outer convection zones. They are analogous to the events on the Sun known as solar flares, which impact our everyday life and modern technological society. Stellar flares, however, can attain much greater energies than those on the Sun. Despite this, we think that these phenomena are rather similar in origin to solar flares, which result from a catastrophic conversion of latent magnetic field energy into atmospheric heating within a region that is relatively small in comparison to normal stellar sizes. We review the last several decades of stellar flare research. We summarize multi-wavelength observational results and the associated thermal and nonthermal processes in flaring stellar atmospheres. Static and hydrodynamic models are reviewed with an emphasis on recent progress in radiation-hydrodynamics and the physical diagnostics in flare spectra. Thanks to their effects on the space weather of exoplanetary systems (and thus in our search for life elsewhere in the universe) and their preponderance in Kepler mission data, white-light stellar flares have re-emerged in the last decade as a widely-impactful area of study within astrophysics. Yet, there is still much we do not understand, both empirically and theoretically, about the spectrum of flare radiation, its origin, and its time evolution. We conclude with several big-picture questions that are fundamental in our pursuit toward a greater understanding of these enigmatic stellar phenomena and, by extension, those on the Sun.

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Optical and X-ray observations of stellar flares on an active M dwarf AD Leonis with the Seimei Telescope, SCAT, NICER, and OISTER

Cited by 60 publications

References 73 publications

Discovery of a Long-Duration Superflare on a Young Solar-Type Star EK Draconis with Nearly Similar Time Evolution for H$α$ and White-Light Emissions

Discovery of a Long-Duration Superflare on a Young Solar-Type Star EK Draconis with Nearly Similar Time Evolution for H$α$ and White-Light Emissions

Explorations of Extreme Space Weather Events from Stellar Observations and Archival Investigations

Stellar flares

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