The Origin of Superflares on G-Type Dwarf Stars of Various Ages

Katsova, M. M.; Livshits, M. A.

doi:10.1007/s11207-015-0752-6

Cited by 21 publications

(14 citation statements)

References 70 publications

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“…On the other hand, the total area typically covered by the system of flare loops is much larger. Contrary to solar flares, in all current analyses of stellar superflares it is assumed that the chromospheric flare condensation is optically thick in the Paschen continuum with a representative temperature 10 4 K which leads to the blackbody WL spectrum (Shibayama et al (2013), Katsova & Livshits (2015), Kowalski et al (2015)). Based on that, one gets relatively small areas which are typically between 0.01 to 1 % of the whole stellar surface (Maehara, private communication).…”

Section: Comments On Spectral Distribution Of Wlmentioning

confidence: 99%

Can Flare Loops Contribute to the White-light Emission of Stellar Superflares?

Heinzel

Shibata

2018

ApJ

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Since the discovery of stellar superflares by Kepler satellite, these extremely energetic events have been studied in analogy to solar flares. Their white-light (WL) continuum emission has been interpreted as being produced by heated ribbons. In this paper we compute the WL emission from overlying flare loops depending on their density and temperature and show that, under conditions expected during superflares, the continuum brightening due to extended loop arcades can significantly contribute to stellar flux detected by Kepler. This requires electron densities in the loops 10 12 − 10 13 cm −3 or higher. We show that such densities, exceeding those typically present in solar flare loops, can be reached on M-dwarf and solar-type superflare stars with large starspots and much stronger magnetic fields. Quite importantly, the WL radiation of loops is not very sensitive to their temperature and thus both cool as well as hot loops may contribute. We show that the WL intensity emergent from optically-thin loops is lower than the blackbody radiation from flare ribbons, but the contribution of loops to total stellar flux can be quite important due to their significant emitting areas. This new scenario for interpreting superflare emission suggests that the observed WL flux is due to a mixture of the ribbon and loop radiation and can be even loop-dominated during the gradual phase of superflares.

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Section: Comments On Spectral Distribution Of Wlmentioning

confidence: 99%

Can Flare Loops Contribute to the White-light Emission of Stellar Superflares?

Heinzel

Shibata

2018

ApJ

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“…The main characteristics of cooler G−type stars, where the Kepler mission detected many superflares, recall the main ingredients at the base of the events subject of the present investigation, i.e., high strength of the magnetic field and strong horizontal velocities. These G−type stars are characterized by an average magnetic field strength higher at least by an order of magnitude than that of the Sun at its maximum of activity (Katsova and Livshits, 2015). showed that many superflares probably occur in large starspots (10 times larger than the largest sunspot) and that the energy of the superflares can be explained by the magnetic energy stored around such starspots .…”

Section: Discussionmentioning

confidence: 99%

“…Furthermore, and to highlight the effect of the photospheric horizontal velocities on the overlying magnetic systems, we follow the approach of Falconer, Moore, and Gary (2002) and Jiang et al (2014) to measure the shear angle, i.e. the angle between the observed horizontal field and the horizontal field derived through a potential field extrapolation.…”

Section: Data and Analysismentioning

confidence: 99%

Conditions for Coronal Observations at the Lijiang Observatory in 2011

et al. 2017

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Recently, two strong homologous white light flares of X-GOES class occurred on the Sun on Sept. 06, 2017, providing a rare exceptional opportunity to study the mechanisms responsible for the formation of the magnetic field configurations suitable for the manifestation of such yet enigmatic eruptive events and their effects in the lower layers of the solar atmosphere. Using photospheric vector magnetograms, taken before the beginning of the two X-class events, as boundary conditions to reconstruct the non−linear coronal magnetic field configuration, we identified two related 3D null points located at low heights above the photosphere (i.e. in very low corona). These null points are most likely responsible for the triggering of the two strong X-GOES class flares. We deduced that their formation at such low altitudes may plausibly be ascribed to the peculiar photospheric horizontal motions of the main magnetic structures of the hosting Active Region NOAA 12673. These events can be adopted as a hint for a possible interpretation of the activity of young G-type stars, recently reported by the Kepler mission. We argued that a possible explanation of the acceleration of huge numbers of particles producing white light emission, during the Sept. 6 events as well as during white light flares in young Sun-like stars, might be attributed to the special accompanying conditions of the occurrence of magnetic reconnection at low altitudes of their atmospheres.SOLA: WLFs_Null3D_SOLA_PHYS.tex; 12 December 2018; 1:32; p. 1 P. Romano et al. et al.

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“…In our observations, we could not find any evidence of Li production by superflares. However, some studies suggest that an increase of Li is only seen just after the end of flare (e.g., [15,16]). In addition, the amount of produced Li by flares may be very small.…”

Section: Abundance and Possibility Of Nucleosynthesis By A Superflarementioning

confidence: 99%

Lithium Abundance of the Solar-Type Superflare Stars

Honda¹,

Notsu²,

Maehara³

et al. 2017

Proceedings of the 14th International Symposium on Nuclei in the Cosmos (NIC2016)

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We performed the high dispersion spectroscopy of solar-type superflare stars with Subaru/HDS, and estimated the stellar parameters and lithium abundance of the stars to compare them with those of the Sun [1]. Our spectroscopic analysis of superflare stars shows more than half of targets have no evidence of binary system and the stellar parameters are in the range of solar-type stars [2,3]. We also investigate the correlations of lithium abundance with stellar atmospheric parameters, rotational velocity, and superflare activities to understand the nature of superflare stars and the possibility of the nucleosynthesis of lithium by superflares. The derived lithium abundance in superflare stars does not show the correlation with stellar parameters. As compared with the lithium abundance in Hyades cluster which is younger than the sun, it is suggested that half of the observed stars are young. However, some objects have the low lithium abundances and slowly rotate on the basis of the estimated v sin i and period of brightness variation. These results indicate that the superflare stars are not only young stars but also old stars like our Sun. In our observations, we could not find the any evidence of lithium productions by superflare.

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The Origin of Superflares on G-Type Dwarf Stars of Various Ages

Cited by 21 publications

References 70 publications

Can Flare Loops Contribute to the White-light Emission of Stellar Superflares?

Can Flare Loops Contribute to the White-light Emission of Stellar Superflares?

Conditions for Coronal Observations at the Lijiang Observatory in 2011

Lithium Abundance of the Solar-Type Superflare Stars

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