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

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 rem...

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Bibliographic Details
Published in:Monthly notices of the Royal Astronomical Society 2005-02, Vol.357 (1), p.251-264
Main Authors: Townsend, R. H. D., Owocki, S. P.
Format: Article
Language:English
Subjects:
stars: chemically peculiar
stars: early-type
stars: emission-line
stars: emission‐line, Be
stars: magnetic fields
stars: mass-loss
stars: rotation
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Summary: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 σ Ori E.
ISSN:0035-8711
1365-2966
DOI:10.1111/j.1365-2966.2005.08642.x