Stellar Winds of T Tauri Stars

Abstract

We present calculations of the structure of magnetized winds of classical T Tauri stars (CTTSs) in an axisymmetric, stationary, polytropic approximation in a given magnetosphere (i.e. the wind dynamics is in general not in force equilibrium with the magnetic flux tubes). According to the widely accepted model of CTTSs (see Camenzind 1990) the magnetosphere is dominated by a strong stellar magnetic field (B* ≃ 1 kG) which possibly is of dipolar type. We obtain the structure of the underlying magnetosphere from a semi-quantitative treatment, in which a dipolar stellar field of kilo-Gauss strength is squeezed by a surrounding diamagnetic accretion disk (Riffert 1980). This approximation allows to derive an analytic expression for the resulting magnetic field. After decreasing according to a dipole in the innermost region the magnetic flux-tube function shows an almost flat behaviour until the collimation region is reached. This picture should yield a reasonably good description for stellar winds, however it does not take into account disk winds. The shape of the resulting flux function poses constraints on the wind parameters and thus on its initial conditions and could give some hints to the origin of the outflows (star and/or accretion disk).