Generalized Multipole X-Wind Model

The X-wind model for magnetospheric accretion and outflow in classical T Tauri stars (CTTS) has gained credence in recent years for a variety of theoretical and observational reasons. However, both this model as well as other theoretical scenarios for explaining magnetospheric disk accretion assume that the stellar field, were it not perturbed by an electrically conducting accretion disk, would have a dipolar geometry (e.g., [5]; OS95 hereafter). Observations of accretion hot spot sizes and net field polarization on the surface of CTTS, however, clearly indicate that the stellar field has a complex multipolar structure. To overcome this discrepancy between theory and data, we reformulate X-wind theory without the dipole constraint. This contribution represents a brief summary of the paper by Mohanty and Shu [6]. In Sect. 1 we present the fundamental physical ideas of the generalized theory, and the associated equations; in Sect. 2 we compare the resulting theoretical prediction to recent observations, and provide some illustrative numerical simulations with multipole stellar fields.