The Hα emission of helium-rich stars

The circumstellar gas of helium-rich stars will be trapped in the outer region of stellar magnetosphere where the centrifugal force dominates. Only in rapidly rotating stars, the outer region can contain the gas much enough to emit the observed H alpha emission energy flux. As the circumstellar gas corotates with the star, the H alpha emission profile becomes very broad and so the emission will appear in the wing of H alpha absorption line which originates in the photosphere of star. (author)