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

Asif ud-Doula; Stanley P. Owocki

doi:10.1086/341543

paper

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

arXiv:astro-ph/0201195 · doi:10.1086/341543

Abstract

We present numerical magnetohydrodynamic (MHD) simulations of the effect of stellar dipole magnetic fields on line-driven wind outflows from hot, luminous stars. Unlike previous fixed-field analyses, the simulations here take full account of the dynamical competition between field and flow, and thus apply to a full range of magnetic field strength, and within both closed and open magnetic topologies. A key result is that the overall degree to which the wind is influenced by the field depends largely on a single, dimensionless, `wind magnetic confinement parameter', $η_{*}$ ( $= B_{e q}^{2} R_{*}^{2} / M ˙ v_{\infty}$ ), which characterizes the ratio between magnetic field energy density and kinetic energy density of the wind. For weak confinement $η_{*} \leq 1$ , the field is fully opened by the wind outflow, but nonetheless for confinements as small as $η_{*} = 1/10$ can have a significant back-influence in enhancing the density and reducing the flow speed near the magnetic equator. For stronger confinement $η_{*} > 1$ , the magnetic field remains closed over a limited range of latitude and height about the equatorial surface, but eventually is opened into a nearly radial configuration at large radii.

39 pages, 9 figures, for better quality figures visit: http://www.bartol.udel.edu/~owocki

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

Abstract

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