Dynamical Simulations of Magnetically Channeled Line-Driven Stellar Winds: II. The Effects of Field-Aligned Rotation

Asif ud-Doula^{1,2}, Stanley P. Owocki^1 and Richard H.D. Townsend^1

1.Bartol Research Institute,
University of Delaware,
Newark, DE 19716
2. Department of Physics and Astronomy,
Swarthmore College,
Swarthmore, PA 19081

Building upon our previous MHD simulation study of magnetic channeling
in radiatively driven stellar winds, we examine here the additional
dynamical effects of stellar {em rotation} in the (still) 2-D axisymmetric
case of an aligned dipole surface field.
In addition to the magnetic confinement parameter $eta_{ast}$
introduced in Paper I, we characterize the stellar rotation in terms of a
parameter $W equiv V_{rm{rot}}/V_{rm{orb}}$ (the ratio of the equatorial surface
rotation speed to orbital speed), examining specifically models with moderately
strong rotation $W =$~0.25 and 0.5, and comparing these to analogous
non-rotating cases.
Defining the associated Alfv'{e}n radius
$R_{rm{A}} approx eta_{ast}^{1/4} Rstar$
and Kepler corotation radius $R_{rm{K}} approx W^{-2/3} Rstar$,
we find rotation effects are weak for models with $R_{rm{A}} < R_{rm{K}}$,
but can be substantial and even dominant for models with $R_{rm{A}} gtwig
In particular, by extending our simulations to magnetic confinement
parameters (up to $eta_{ast} = 1000$)
that are well above those ($eta_{ast} = 10$)
considered in Paper I, we are able to study cases with $R_{rm{A}} gg
we find that these do indeed show clear formation of the
{em rigid-body} disk predicted in previous analytic models,
with however a rather complex, dynamic behavior characterized by both
episodes of downward infall and outward breakout that limit the
buildup of disk mass.
Overall, the results provide an intriguing glimpse into the complex
interplay between rotation and magnetic confinement, and form the
basis for a full MHD description of the rigid-body disks expected in
strongly magnetic Bp stars like $sigma$~Ori~E.

Reference: MNRAS (in press)
Status: Manuscript has been accepted

Weblink: http://shayol.bartol.udel.edu/massivewiki-media/publications/rotation.pdf


Email: asif@bartol.udel.edu