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It is suggested that Beals's Type III P Cygni profiles, in which additional emission appears blueward of the blueshifted absorption feature, may be produced in stars in which the inner parts of the expanding envelope (stellar wind) are forced into corotation with the star out to a few stellar radii by a weak global magnetic field. Numerical estimates are made for the O4ef star Xi Pup which suggest that the Alfvenic radius (limit of corotation) is about 2.1 stellar radii, and that the required magnetic field at that point is about 70 Gauss. The braking time scale implied by angular momentum loss to the wind is short compared with the main-sequence (hydrogen core-burning) lifetime of the star and the present high mass loss rate.
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Mihalas et al. (1980) studied this question.
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