Dynamical Simulations of Magnetically Channeled Line-driven Stellar Winds. I. Isothermal, Nonrotating, Radially Driven Flow

摘要: We present numerical magnetohydrodynamic (MHD) simulations of the effect stellar dipole magnetic fields on line-driven wind outflows from hot, luminous stars. Unlike previous fixed-field analyses, here take full account dynamical competition between field and flow thus apply to a range strength within both closed open topologies. A key result is that overall degree which influenced by depends largely single, dimensionless confinement parameter η* (= BR/v∞), characterizes ratio energy density kinetic wind. For weak confinement, ≤ 1, fully opened outflow, but nonetheless, for confinements as small = 1/10 it can have significant back-influence in enhancing reducing speed near equator. stronger > remains over limited latitude height about equatorial surface, eventually into nearly radial configuration at large radii. Within loops, channeled toward loop tops shock collisions are strong enough produce hard X-rays, with stagnated material then pulled gravity back onto star quite complex variable inflow patterns. flow, channeling leads oblique shocks again X-rays also lead thin, dense, slowly outflowing disk The polar characterized faster-than-radial expansion more gradual than anticipated one-dimensional tube analyses much modest increase terminal (less 30%), consistent observational constraints. Overall, results provide groundwork interpreting many types observations—e.g., UV line profile variability, redshifted absorption or emission features, enhanced density-squared emission, X-ray emission—that might be associated perturbation hot-star winds surface fields.