http://arxiv.org/abs/2007.00040
The magnetic activity of late-type stars is correlated with their rotation rates. Up to a certain limit, stars with smaller Rossby numbers, defined as the rotation period divided by the convective turnover time, have higher activity. A more detailed look at this rotation-activity relation reveals that, rather than being a simple power law relation, the activity scaling has a shallower slope for the low-Rossby stars than for the high-Rossby ones. We find that, for the chromospheric CaII H&K activity, this scaling relation is well modelled by a broken two-piece power law. Furthermore, the knee-point of the relation coincides with the axisymmetry to non-axisymmetry transition seen in both the spot activity and surface magnetic field configuration of active stars. We interpret this knee-point as a dynamo transition between dominating axi- and non-axisymmetric dynamo regimes with a different dependence on rotation and discuss this hypothesis in the light of current numerical dynamo models.
J. Lehtinen, M. Käpylä, N. Olspert, et. al.
Thu, 2 Jul 20
30/64
Comments: 8 pages, 4+1 figures, 1 table, submitted to ApJL
You must be logged in to post a comment.