Frequencies of Superflares in Solar-Type Stars Detected by the Kepler Orbital Observatory

Akopian, A. A.

doi:10.1007/s10511-013-9302-9

Cited by 6 publications

(8 citation statements)

References 9 publications

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“…We emphasise that we are not implying that the stars in the nonvariable sample are intrinsically without flare activity, only that they have not produced detectable flares in the 2XMM survey observations, and we note that this result is broadly consistent with estimates based on Poisson statistics (e.g. Akopian 2013). The data used in the current analysis were insufficient in terms of total observing time for each star to fully resolve issue (i), or to address the related topic of degree of correlation, if any, between flares closely-spaced in time.…”

Section: Flare Rates and Duty Cyclessupporting

confidence: 85%

A survey of stellar X-ray flares from theXMM-Newtonserendipitous source catalogue: HIPPARCOS-Tycho cool stars

Pye

Rosen

Fyfe

et al. 2015

A&A

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Context. The X-ray emission from flares on cool (i.e. spectral-type F-M) stars is indicative of very energetic, transient phenomena, associated with energy release via magnetic reconnection. Aims. We present a uniform, large-scale survey of X-ray flare emission. The XMM-Newton Serendipitous Source Catalogue and its associated data products provide an excellent basis for a comprehensive and sensitive survey of stellar flares -both from targeted active stars and from those observed serendipitously in the half-degree diameter field-of-view of each observation. Methods. The 2XMM Catalogue and the associated time-series ("light-curve") data products have been used as the basis for a survey of X-ray flares from cool stars in the Hipparcos-Tycho-2 catalogue. In addition, we have generated and analysed spectrally-resolved (i.e. hardness-ratio), X-ray light-curves. Where available, we have compared XMM OM UV/optical data with the X-ray light-curves. Results. Our sample contains ∼130 flares with well-observed profiles; they originate from ∼70 stars. The flares range in duration from ∼10 3 to ∼10 4 s, have peak X-ray fluxes from ∼10 −13 to ∼10 −11 erg cm −2 s −1 , peak X-ray luminosities from ∼10 29 to ∼10 32 erg s −1 , and X-ray energy output from ∼10 32 to ∼10 35 erg. Most of the ∼30 serendipitously-observed stars have little previously reported information. The hardness-ratio plots clearly illustrate the spectral (and hence inferred temperature) variations characteristic of many flares, and provide an easily accessible overview of the data. We present flare frequency distributions from both target and serendipitous observations. The latter provide an unbiased (with respect to stellar activity) study of flare energetics; in addition, they allow us to predict numbers of stellar flares that may be detected in future X-ray wide-field surveys. The serendipitous sample demonstrates the need for care when calculating flaring rates, especially when normalising the number of flares to a total exposure time, where it is important to consider both the stars seen to flare and those from which variability was not detected (i.e. measured as non-variable), since in our survey, the latter outnumber the former by more than a factor ten. The serendipitous variable and "non-variable" stars appear very similar in terms of the distributions of general properties such as quiescent X-ray luminosity; from the available data, it is unclear whether the distinction by flaring is due to an additional, intrinsic property such as intra-system interactions in a close binary system, or is simply the result of limited observations and detection thresholds on a random flaring process, with no real difference between the two samples, or may be a combination of these effects. However, the number of detected flares compared with the number of stars not seen to vary is broadly consistent with estimates based on Poisson statistics.

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Section: Flare Rates and Duty Cyclessupporting

confidence: 85%

A survey of stellar X-ray flares from theXMM-Newtonserendipitous source catalogue: HIPPARCOS-Tycho cool stars

Pye

Rosen

Fyfe

et al. 2015

A&A

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“…Independent of the GL method, the analysis described in Akopian () was performed to the flare occurrence times, where a cyclic intensity function was fitted to the data (Daley & Vere‐Jones, 2003; Kutoyants, 1980).…”

Section: Data Analysis and Resultsmentioning

confidence: 99%

“…From exploring a small subsample of stars that most frequently flared within the list of Maehara (), Akopian () found a statistically significant change of the flare frequency for the star KIC007264976. However, the data presented in Maehara et al () could not reveal any cyclic variability because of the relatively small number of flares.…”

Section: Introductionmentioning

confidence: 99%

KIC011764567: An evolved Kepler‐star showing substantial flare activity

et al. 2017

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We intensively studied the flare activity on the stellar object KIC011764567. The star was thought to be a solar type, with a temperature of T eff ≈ (5640 ± 200) K, log(g) = (4.3 ± 0.3) dex, and a rotational period of P rot ≈ 22 days. High-resolution spectra turn the target to an evolved object with T eff = (5300 ± 150) K, a metalicity of [m/H] = (−0.5 ± 0.2), a surface gravity of log(g) = (3.3 ± 0.4) dex, and a projected rotational velocity of v sin i = (22 ± 1) km s −1 . Within an observing time span of 4 years, we detected 150 flares in Kepler data in the energy range 10 36 -10 37 erg. From a dynamical Lomb-Scargle periodogram, we have evidence for differential rotation as well as for stellar spot evolution and migration. On analyzing the occurrence times of the flares, we found hints for a periodic flare frequency cycle of 430-460 days, a significant increase with an increase in threshold of the flares' equivalent duration. One explanation is a very short activity cycle of the star with that period. Another possibility, also proposed by others in similar cases, is that the larger flares may be triggered by external phenomena, such as magnetic interaction with an unseen companion. Our high-resolution spectra show that KIC011764567 is not a short-period binary star.

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“…Recently it was used in studies of new flare stars system in open cluster M37 (Chang et al, 2015) and other celestial objects that are closely related to the flare stars and flare phenomenon (Akopian, 2013(Akopian, , 2017Pye et al, 2015). More recently, the Ambartsumian estimator was applied to solar-type stars with very powerful flares (called superflares).…”

Section: Recent Applications Of Ambartsumian Estimatormentioning

confidence: 99%

“…Considering the data obtained by the orbital observatory "Kepler", Maehara et al(2012) have registered 365 superflares on 148 stars, including some from slowly rotating solar-type stars, from about 83,000 stars observed over 120 days. With these data it was estimated the number of stars producing superflares (Akopian, 2013).…”

Section: Recent Applications Of Ambartsumian Estimatormentioning

confidence: 99%

Review on the astronomical estimators of number of flare stars

Akopian¹,

Observatory²

2018

ComBAO

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Review is devoted to estimators introduced in astronomy by Ambartsumian and his followers that are used to estimating the unknown number of flare stars and other randomly flashing objects (stars with X-ray flares, solar type stars with superflares). Some important astronomical applications of them are presented. The development of these methods in astronomy have proceeded regardless of development of analogous methods of mathematical statistics. Brief history of this development and parallels with similar statistical methods is presented.

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Frequencies of Superflares in Solar-Type Stars Detected by the Kepler Orbital Observatory

Cited by 6 publications

References 9 publications

A survey of stellar X-ray flares from theXMM-Newtonserendipitous source catalogue: HIPPARCOS-Tycho cool stars

A survey of stellar X-ray flares from theXMM-Newtonserendipitous source catalogue: HIPPARCOS-Tycho cool stars

KIC011764567: An evolved Kepler‐star showing substantial flare activity

Review on the astronomical estimators of number of flare stars

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