Superflares on the slowly rotating solar-type stars KIC10524994 and KIC07133671?

TL;DR

This study analyzes Kepler data for two sun-like stars, identifying superflares and investigating their origins, revealing that some superflares may originate from nearby stars rather than the stars themselves, affecting superflare rate estimates.

Contribution

It provides a detailed analysis of superflare occurrences on two solar twins and demonstrates that some superflares originate from neighboring stars, refining superflare frequency estimates.

Findings

Four new superflares detected on KIC10524994.

Astrometric data suggests superflares on KIC07133671 originate from a nearby star.

Superflare rate for sun-like stars may be overestimated due to contamination.

Abstract

An investigation of the G-type stellar population with Kepler (as done by Maehara et al.) shows that less than 1 per cent of those stars show superflares. Due to the large pixel scale of Kepler ($\sim4 arcsec \: px^{-1}$), it is still not clear whether the detected superflares really occur on the G-type stars. Knowing the origin of such large brightenings is important to study their frequency statistics, which are uncertain due to the low number of sun-like stars ($T_{eff} = 5600-6000 \:K$ and $P_{rot} > 10 \:d$) which are currently considered to exhibit superflares. We present a complete Kepler data analysis of the sun-like stars KIC10524994 and KIC07133671 (the only two stars within this subsample of solar twins with flare energies larger than $10^{35}$ erg; Maehara et al.), regarding superflare properties and a study about their origin. We could detect four new superflares within the epoch Maehara et al. investigated and found 14 superflares in the remaining light curve for KIC10524994. Astrometric Kepler data of KIC07133671 show that the photocentre is shifted by 0.006 px or 25 mas during the one detected flare. Hence, the flare probably originated from another star directed towards the north-east. This lowers the superflare rate of sun-like stars (and hence the Sun) for $E > 10^{35}$ erg, since this additional star is probably not solar-like.