Formulating Mass-loss Rates for Sun-like Stars: A Hybrid Model Approach

We observe an enhanced stellar wind mass-loss rate from low-mass stars exhibiting higher X-ray flux. This trend, however, does not align with the Sun, where no evident correlation between X-ray flux and mass-loss rate is present. To reconcile these observations, we propose a hybrid model for the stellar wind from solar-type stars, incorporating both Alfven wave dynamics and flux emergence-driven interchange reconnection, an increasingly studied concept guided by the latest heliospheric observations. For establishing a mass-loss rate scaling law, we perform a series of magnetohydrodynamic simulations across varied magnetic activities. Through a parameter survey concerning the surface (unsigned) magnetic flux (phi surf) and the open-to-surface magnetic flux ratio (xi open = phi open/phi surf), we derive a scaling law of the mass-loss rate given by Mw/Mw,circle dot=phi surf/phi circle dot surf0.52 xi open/xi circle dot open0.86 , where Mw,circle dot=2.0x10-14M circle dot yr-1 , phi circle dot surf=3.0x1023Mx , and xi circle dot open=0.2 . By comparing cases with and without flux emergence, we find that the increase in the mass-loss rate with the surface magnetic flux can be attributed to the influence of flux emergence. Our scaling law demonstrates an agreement with solar wind observations spanning 40 yr, exhibiting superior performance when compared to X-ray-based estimations. Our findings suggest that flux emergence may play a significant role in the stellar winds of low-mass stars, particularly those originating from magnetically active stars.