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Paper: A Magnetic Rotator Wind-Disk Model for Be Stars
Volume: 337, The Nature and Evolution of Disks Around Hot Stars
Page: 259
Authors: Maheswaran, M.
Abstract: We consider a Magnetic Rotator Wind-Disk(MRWD) model for the formation of Keplerian disks around Be stars. Material from low latitudes of the stellar surface flows along magnetic flux tubes and passes through a shock surface near the equatorial plane to form a pre-Keplerian disk region. Initially, the density in this region is small and the magnetic field helps to maintain super-Keplerian rotation speeds. After a fill-up time, the density of the disk is significantly larger and the magnetic force in this region becomes negligible compared with the centrifugal force. The material then moves outwards to form a quasi-steady Keplerian disk. During the fill-up stage, the meridional component Bm,* of the magnetic field at the stellar surface must be larger than a minimum value Bm,*,min . The radial extent of the quasi-steady Keplerian region will be larger when Bm,* is larger or when viscosity plays a role. In B-type stars, the values of Bm,*,min are of order 1 G to 10 G. We find that a condition for the formation of shock-compressed disk regions is that in faster rotating stars, the wind speed must be correspondingly larger.
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