Three-dimensional Numerical Simulations of Magnetized Winds of Solar-like Stars

By means of self-consistent three-dimensional (3D) magnetohydrodynamics (MHD) numerical simulations, we analyze magnetized solar-like stellar winds and their dependence on the plasma-β parameter (the ratio between thermal and magnetic energy densities). This is the first study to perform such analysis solving the fully ideal 3D MHD equations. We adopt in our simulations a heating parameter described by γ, which is responsible for the thermal acceleration of the wind. We analyze winds with polar magnetic field intensities ranging from 1 to 20 G. We show that the wind structure presents characteristics that are similar to the solar coronal wind. The steady-state magnetic field topology for all cases is similar, presenting a configuration of helmet streamer-type, with zones of closed field lines and open field lines coexisting. Higher magnetic field intensities lead to faster and hotter winds. For the maximum magnetic intensity simulated of 20 G and solar coronal base density, the wind velocity reaches values of ∼ 1000 km s at r ∼ 20 r0 and a maximum temperature of ∼ 6×10 6 K at r ∼ 6 r0. The increase of the field intensity generates a larger “dead zone” in the wind, i. e., the closed loops that inhibit matter to escape from latitudes lower than ∼ 45 extend farther away from the star. The Lorentz force leads naturally to a latitude-dependent wind. We show that by increasing the density and maintaining B0 = 20 G, the system recover back to slower and cooler winds. For a fixed γ, we show that the key parameter in determining the wind velocity profile is the β-parameter at the coronal base. Therefore, there is a group of magnetized flows that would present the same terminal velocity despite of its thermal and magnetic energy densities, as long as the plasma-β parameter is the same. This degeneracy, however, can be removed if we compare other physical parameters of the wind, such as the mass-loss rate. We analyze the influence of γ in our results and we show that it is also important in determining the wind structure. Subject headings: stars: winds, outflows – MHD – methods: numerical – stars: late-type