Can superflares occur on the Sun? : a view from dynamo theory
|Author:||Katsova, M. M.1; Kitchatinov, L. L.2,3; Livshits, M. A.4;|
1Sternberg State Astronomical Institute, Lomonosov Moscow State University, Moscow, 119991 Russia
2Institute for Solar-Terrestrial Physics, PO Box 291, Irkutsk, 664033 Russia
3Pulkovo Astronomical Observatory, St. Petersburg, 196140 Russia
4IZMIRAN, Troitsk, Moscow, 108840 Russia
5School of Mathematics, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
6Department of Physics, Moscow State University, Moscow, 119992 Russia
7Space Climate Research Unit and Sodankylä Geophysical Observatory, University of Oulu, 90014 Finland
|Online Access:||PDF Full Text (PDF, 0.2 MB)|
|Persistent link:|| http://urn.fi/urn:nbn:fi-fe201803073898
|Publish Date:|| 2018-03-07
Recent data from the Kepler mission has revealed the occurrence of superflares in Sun-like stars which exceed by far any observed solar flares in released energy. Radionuclide data do not provide evidence for occurrence of superflares on the Sun over the past eleven millennia. Stellar data for a subgroup of superflaring Kepler stars are analysed in an attempt to find possible progenitors of their abnormal magnetic activity. A natural idea is that the dynamo mechanism in superflaring stars differs in some respect from that in the Sun. We search for a difference in the dynamo-related parameters between superflaring stars and the Sun to suggest a dynamo mechanism as close as possible to the conventional solar/stellar dynamo but capable of providing much higher magnetic energy. Dynamo based on joint action of differential rotation and mirror asymmetric motions can in principle result in excitation of two types of magnetic fields. First of all, it is well-known in solar physics dynamo waves. The point is that another magnetic configuration with initial growth and further stabilisation can also be excited. For comparable conditions, magnetic field of second configuration is much stronger than that of the first one just because dynamo does not spend its energy for periodic magnetic field inversions but uses it for magnetic field growth. We analysed available data from the Kepler mission concerning the superflaring stars in order to find tracers of anomalous magnetic activity. As suggested in a recent paper , we find that anti-solar differential rotation or anti-solar sign of the mirror-asymmetry of stellar convection can provide the desired strong magnetic field in dynamo models. We confirm this concept by numerical models of stellar dynamos with corresponding governing parameters. We conclude that the proposed mechanism can plausibly explain the superflaring events at least for some cool stars, including binaries, subgiants and, possibly, low-mass stars and young rapid rotators.
Original Russian Text © M.M. Katsova, L.L. Kitchatinov, M.A. Livshits, D.L. Moss, D.D. Sokoloff, I.G. Usoskin, 2018, published in Astronomicheskii Zhurnal, 2018, Vol. 95, No. 1, pp. 78–87.
|Pages:||72 - 80|
|Type of Publication:||
A1 Journal article – refereed
|Field of Science:||
115 Astronomy and space science
DS acknowledges financial support from RFBR under grant 15-02-01407. IU’s contribution was made in the framework of ReSoLVE Centre of Excellence (Academy of Finland, project no. 272157). LLK is thankful to the Russian Foundation for Basic Research for the support (project 17-02-00016). MMK is grateful to the RFBR (grant 15-02-06271) and the Leading Scientific Schools project 9570.2016.2 for financial support.
|Academy of Finland Grant Number:||
272157 (Academy of Finland Funding decision)
© Pleiades Publishing, Ltd. 2018. Published in this repository with the kind permission of the publisher.