[Triumf-seminars] TRIUMF Theory Seminar today at 13:00

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Date/Time: Tue 2010-09-21 at 13:00

Location:  Theory Room         

Speaker:   Anand Thirumalai (UBC)

Title:     Hybrid MHD-dust-driven winds of evolved stars - A new perspective

Abstract: The winds of evolved stars have hitherto been modelled using either a purely radiation-hydrodynamics models with dust or by employing pure-magnetohydrodynamic (MHD) effluxes. There are problems with both pictures. The first kind does not take into account that stars have magnetic fields, which can be responsible for shaping the outflows in a substantial way. Concordantly, the latter kind of models disregard the formation of dust in the cool envelops of these dying stars, which through their opacity absorb much of the stellar luminosity, thereby gaining sufficient impetus to drive massive winds as they move through the gas. Herein, we present calculations for a new magnetised hybrid wind model for Asymptotic Giant Branch (AGB) stars. The model incorporates a canonical Weber-Davis (WD) stellar wind with dust grains in the envelope of an AGB star. The resulting hybrid picture preserves traits of both types of winds. It is seen that this combination requires that the dust-parameter ($\Gamma_{d}$) be less than unity in order to achieve an outflow. The emergence of magnetosonic critical points in the wind changes the nature of the dust-driven outflow, simultaneously, the presence of a dust condensation radius changes the morphology of the MHD solutions for the wind. In this context, we additionally investigate the effect of having magnetic-cold spots on the equator of an AGB star and its implications for dust formation.



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