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Superflare occurrence and energies on G-, K-, and M-type dwarfs
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden .
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden .ORCID iD: 0000-0002-7304-021X
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2014 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 792, no 1, 67- p.Article in journal (Refereed) Published
Abstract [en]

Kepler data from G-, K-, and M-type stars are used to study conditions that lead to superflares with energies above 10(34) erg. From the 117,661 stars included, 380 show superflares with a total of 1690 such events. We study whether parameters, like effective temperature or rotation rate, have any effect on the superflare occurrence rate or energy. With increasing effective temperature we observe a decrease in the superflare rate, which is analogous to the previous findings of a decrease in dynamo activity with increasing effective temperature. For slowly rotating stars, we find a quadratic increase of the mean occurrence rate with the rotation rate up to a critical point, after which the rate decreases linearly. Motivated by standard dynamo theory, we study the behavior of the relative starspot coverage, approximated as the relative brightness variation. For faster rotating stars, an increased fraction of stars shows higher spot coverage, which leads to higher superflare rates. A turbulent dynamo is used to study the dependence of the Ohmic dissipation as a proxy of the flare energy on the differential rotation or shear rate. The resulting statistics of the dissipation energy as a function of dynamo number is similar to the observed flare statistics as a function of the inverse Rossby number and shows similarly strong fluctuations. This supports the idea that superflares might well be possible for solar-type G stars.

Place, publisher, year, edition, pages
2014. Vol. 792, no 1, 67- p.
Keyword [en]
activity stars, flare stars, rotation starspots stars, stars, statistics dynamo
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:kth:diva-152565DOI: 10.1088/0004-637X/792/1/67ISI: 000341172100067ScopusID: 2-s2.0-84906223678OAI: diva2:750510
EU, European Research Council, 227952Swedish Research Council, 621-2011-5076 2012-5797

QC 20140929

Available from: 2014-09-29 Created: 2014-09-29 Last updated: 2014-09-29Bibliographically approved

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