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Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Indian Institute of Science (IISC), India.
2014 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 791, no 1, 59- p.Article in journal (Refereed) Published
Abstract [en]

We attempt to provide a quantitative theoretical explanation for the observations that Ca II H/K emission and X-ray emission from solar-like stars increase with decreasing Rossby number (i.e., with faster rotation). Assuming that these emissions are caused by magnetic cycles similar to the sunspot cycle, we construct flux transport dynamo models of 1M(circle dot) stars rotating with different rotation periods. We first compute the differential rotation and the meridional circulation inside these stars from a mean-field hydrodynamics model. Then these are substituted in our dynamo code to produce periodic solutions. We find that the dimensionless amplitude f(m) of the toroidal flux through the star increases with decreasing rotation period. The observational data can be matched if we assume the emissions to go as the power 3-4 of f(m). Assuming that the Babcock-Leighton mechanism saturates with increasing rotation, we can provide an explanation for the observed saturation of emission at low Rossby numbers. The main failure of our model is that it predicts an increase of the magnetic cycle period with increasing rotation rate, which is the opposite of what is found observationally. Much of our calculations are based on the assumption that the magnetic buoyancy makes the magnetic flux tubes rise radially from the bottom of the convection zone. Taking into account the fact that the Coriolis force diverts the magnetic flux tubes to rise parallel to the rotation axis in rapidly rotating stars, the results do not change qualitatively.

Place, publisher, year, edition, pages
2014. Vol. 791, no 1, 59- p.
Keyword [en]
dynamo, magnetohydrodynamics (MHD), stars: activity, stars: magnetic field, Sun: activity, Sun: magnetic fields, Sun: X-rays, gamma rays
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:su:diva-107103DOI: 10.1088/0004-637X/791/1/59ISI: 000339657700059OAI: diva2:743908


Available from: 2014-09-05 Created: 2014-09-03 Last updated: 2014-09-05Bibliographically approved

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