A rigidly rotating magnetosphere model for circumstellar emission from magnetic OB stars

R. H. D. Townsend$^{1,2}$ and
S. P. Owocki$^{1}$

1 - Bartol Research Institute, University of Delaware, Newark, DE 19716, USA; 2 - University College London, Gower Street, London, WC1E 6BT, UK

We present a semi-analytical approach for modelling circumstellar
emission from rotating hot stars with a strong dipole magnetic field
tilted at an arbitrary angle to the rotation axis. By assuming the
rigid-field limit in which material driven (e.g. in a wind outflow)
from the star is forced to remain in strict rigid-body corotation, we
are able to solve for the effective centrifugal-plus-gravitational
potential along each field line, and thereby identify the location of
potential minima where material is prone to accumulate. Applying basic
scalings for the surface mass flux of a radiatively driven stellar
wind, we calculate the circumstellar density distribution that obtains
once ejected plasma settles into hydrostatic stratification along
field lines. The resulting accumulation surface resembles a rigidly
rotating, warped disc, tilted such that its average surface normal
lies between the rotation and magnetic axes. Using a simple model of
the plasma emissivity, we calculate time-resolved synthetic line
spectra for the disc. Initial comparisons show an encouraging level of
correspondence with the observed rotational phase variations of
Balmer-line emission profiles from magnetic Bp stars such as $\sigma$
Ori E.

Reference: 2005, MNRAS, 357, 251
Status: Manuscript has been accepted