TY - JOUR
T1 - Superflares on the late-type giant KIC 2852961
T2 - Scaling effect behind flaring at different energy levels
AU - Kovári, Zs
AU - Oláh, K.
AU - Günther, M. N.
AU - Vida, K.
AU - Kriskovics, L.
AU - Seli, B.
AU - Bakos, G. A.
AU - Hartman, J. D.
AU - Csubry, Z.
AU - Bhatti, W.
N1 - Funding Information:
Acknowledgements. Authors are grateful to the anonymous referee for his/her valuable comments which helped to improve the manuscript. Authors thank Andrew Vanderburg at Harvard Smithsonian Center for Astrophysics for his help in understanding the action of Presearch Data Conditioning (PDC) module in Kepler data processing. This work was supported by the Hungarian National Research, Development and Innovation Office grant OTKA K131508, KH-130526 and by the Lendület Program of the Hungarian Academy of Sciences, project No. LP2018-7/2019. Authors from Konkoly Observatory acknowledge the financial support of the Austrian-Hungarian Action Foundation (95 öu3, 98öu5, 101öu13). M.N.G. acknowledges support from MIT’s Kavli Institute as a Torres postdoctoral fellow. Data presented in this paper are based on observations obtained with the Hungarian-made Automated Telescope Network, with stations at the Submillimeter Array of the Smithsonian Astrophysical Observatory (SAO), and at the Fred Lawrence Whipple Observatory of SAO. IRAF used in this work was distributed by the National Optical Astronomy Observatory, which was managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. This work presents results from the European Space Agency (ESA) space mission Gaia. Gaia data are being processed by the Gaia Data Processing and Analysis Consortium (DPAC). Funding for the DPAC is provided by national institutions, in particular the institutions participating in the Gaia MultiLateral Agreement (MLA). The Gaia mission website is https://www.cosmos.esa. int/gaia. The Gaia archive website is https://archives.esac.esa.int/ gaia.
Publisher Copyright:
© ESO 2020.
PY - 2020/9/1
Y1 - 2020/9/1
N2 - Context. The most powerful superflares reaching 1039 erg bolometric energy are from giant stars. The mechanism behind flaring is thought to be the magnetic reconnection, which is closely related to magnetic activity (including starspots). However, it is poorly understood how the underlying magnetic dynamo works and how the flare activity is related to the stellar properties that eventually control the dynamo action. Aims. We analyze the flaring activity of KIC 2852961, a late-type giant star, in order to understand how its flare statistics are related to those of other stars with flares and superflares, and to understand the role of the observed stellar properties in generating flares. Methods. We searched for flares in the full Kepler dataset of KIC 2852961 using an automated technique together with visual inspection. We cross-matched the flare-like events detected by the two different approaches and set a final list of 59 verified flares during the observing term. We calculated flare energies for the sample and performed a statistical analysis. Results. The stellar properties of KIC 2852961 are revised and a more consistent set of parameters are proposed. The cumulative flare energy distribution can be characterized by a broken power law; that is to say, on the log-log representation the distribution function is fitted by two linear functions with different slopes, depending on the energy range fitted. We find that the total flare energy integrated over a few rotation periods correlates with the average amplitude of the rotational modulation due to starspots. Conclusions. Flares and superflares seem to be the result of the same physical mechanism at different energy levels, also implying that late-type stars in the main sequence and flaring giant stars have the same underlying physical process for emitting flares. There might be a scaling effect behind the generation of flares and superflares in the sense that the higher the magnetic activity, the higher the overall magnetic energy released by flares and/or superflares.
AB - Context. The most powerful superflares reaching 1039 erg bolometric energy are from giant stars. The mechanism behind flaring is thought to be the magnetic reconnection, which is closely related to magnetic activity (including starspots). However, it is poorly understood how the underlying magnetic dynamo works and how the flare activity is related to the stellar properties that eventually control the dynamo action. Aims. We analyze the flaring activity of KIC 2852961, a late-type giant star, in order to understand how its flare statistics are related to those of other stars with flares and superflares, and to understand the role of the observed stellar properties in generating flares. Methods. We searched for flares in the full Kepler dataset of KIC 2852961 using an automated technique together with visual inspection. We cross-matched the flare-like events detected by the two different approaches and set a final list of 59 verified flares during the observing term. We calculated flare energies for the sample and performed a statistical analysis. Results. The stellar properties of KIC 2852961 are revised and a more consistent set of parameters are proposed. The cumulative flare energy distribution can be characterized by a broken power law; that is to say, on the log-log representation the distribution function is fitted by two linear functions with different slopes, depending on the energy range fitted. We find that the total flare energy integrated over a few rotation periods correlates with the average amplitude of the rotational modulation due to starspots. Conclusions. Flares and superflares seem to be the result of the same physical mechanism at different energy levels, also implying that late-type stars in the main sequence and flaring giant stars have the same underlying physical process for emitting flares. There might be a scaling effect behind the generation of flares and superflares in the sense that the higher the magnetic activity, the higher the overall magnetic energy released by flares and/or superflares.
KW - Stars: activity
KW - Stars: flare
KW - Stars: individual: 2MASS J19261136+3803107
KW - Stars: individual: KIC 2852961
KW - Stars: individual: TIC 137220334
KW - Stars: late-type
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U2 - 10.1051/0004-6361/202038397
DO - 10.1051/0004-6361/202038397
M3 - Article
AN - SCOPUS:85091894365
SN - 0004-6361
VL - 641
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
M1 - A83
ER -