Solar and stellar flares: frequency, active regions and stellar dynamo

Abstract

We demonstrate that for weak flares the dependence on spottedness can be rather weak. The fact is that such flares can occur both in small and large active regions. At the same time, powerful large flares of classes M and X occur much more often in large active regions. In energy estimates, the mean magnetic field in starspots can also be assumed equal to the mean field in the sunspot umbra. So the effective mean magnetic field is 900 Mx/cm${}^2$ in sunspots and 2000 Mx/cm${}^2$ in starspots. Moreover, the height of the energy storage cannot be strictly proportional to A${}^{1/2}$. For stars, the fitting factor is an order of magnitude smaller. The analysis of the occurrence rate of powerful solar X-ray flares of class M and X and superflares on stars shows that, with allowance for the difference in the spottedness and compactness of active regions, both sets can be described by a single model. Thus, the problem of superflares on stars and their absence on the Sun is reduced to the problem of difference in the effectiveness of the dynamo mechanisms.

15 pages, 4 figures, 1 table. Accepted to ApJ

References in corpus (18)

• The case for a distributed solar dynamo shaped by near-surface shear
• The H$\alpha$ emission of nearby M dwarfs and its relation to stellar rotation
• Non-linear force-free field modeling of a solar active region around the time of a major flare and coronal mass ejection
• The solar magnetic field
• Flare-productive active regions
• Statistical properties of superflares on solar-type stars based on 1-min cadence data
• Statistical Properties of Superflares on Solar-type Stars: Results Using All of the Kepler Primary Mission Data
• Global Energetics of Solar Flares: I. Magnetic Energies
• Superflares, chromospheric activities and photometric variabilities of solar-type stars from the second-year observation of TESS and spectra of LAMOST
• From Starspots to Stellar Coronal Mass Ejections -- Revisiting Empirical Stellar Relations
• Search for flares and associated CMEs on late-type main-sequence stars in optical SDSS spectra
• A Statistical Study of Photospheric Magnetic Field Changes During 75 Solar Flares
• A distinct magnetic property of the inner penumbral boundary. II. Formation of a penumbra at the expense of a pore
• The morphology of average solar flare time profiles from observations of the Sun's lower atmosphere
• Short term variability of DS Tuc A observed with TESS
• Characterization of the umbra-penumbra boundary by the vertical component of the magnetic field -- Analysis of ground-based data from the GREGOR Infrared Spectrograph
• Properties of Kepler Stars with the Most Powerful Flares
• Detection of Optical Flares on the Selected G-M Dwarfs from Long-term Photometric Series