Simulations of the Photospheric Magnetic Activity and Outer Atmospheric Radiative Losses of Cool Stars Based on Characteristics of the Solar Magnetic Field

Abstract

The observed disk-integrated radiative losses from the outer atmospheres of stars with convective envelopes are determined by the distribution of magnetic field over their surfaces. Earlier modeling of the random walk transport of the solar photospheric magnetic field with the classical Leighton model has given us insight into how field patterns form and evolve on large scales. This paper presents the first comprehensive simulations of the dynamic photospheric magnetic field of the Sun down to the scale of the mixed polarity network, thus incorporating all flux involved in outer atmospheric heating. The algorithm incorporates the classical diffusion model but includes ephemeral regions (which populate the network that contributes significantly to the disk-integrated chromospheric emission) and the early phase of decay of active regions (which is important for the field patterns in very active stars). Moreover, individual flux concentrations are tracked and subjected to collisions and fragmentation, and the flux dispersal is made dependent on the flux contained in the concentrations, as observed on the Sun. The latter modification causes the model to be nonlinear. Tests demonstrate that the new model successfully describes the solar magnetic field.