Quasi-emission lines in rotating B stars

Abstract

Theorical line profiles for rotating B stars have been calculated in an effort to explain recent observations of quasi-emission bumps in the cores of some absorption lines. It is found that, assuming the stellar atmospheres are in LTE, purely rotational effects alone cannot account for the observations. Subsequently, it is verified that an equator-to-pole reduction in absorption-line equivalent width by a sufficent amount can produce a central reversal in the convolved line profile, but that its strength depends on both the reduction factor and the intrinsic line-width. Allowing that such an equivalent width variation is caused by a variation in effective temperature, observed line profiles can be reproduced by introducing a cold polar cap.