On mechanisms separating stars into normal and chemically peculiar

Abstract

The paper argues in favor of the assumption that magnetic and non-magnetic protostars, from which CP stars were formed, are the objects that had rotation velocities of the parent cloud V smaller than a critical value V_c. At V greater than the critical value, differential rotation emerges in the collapsing protostellar cloud, which twists magnetic lines of force into an’ invisible’ toroidal shape and disturbs the stability of the atmosphere. In magnetic protostars, the loss of angular momentum is due to magnetic braking, while in metallic protostars, the loss of rotation momentum occurs due to tidal interactions with a close component. HgMn stars are most likely not affected by some braking mechanism, but originated from the slowest protostellar rotators. The boundary of V_c where the differential rotation occurs is not sharp. The slower the protostar rotates, the greater the probability of suppressing the differential rotation and the more likely the possibility of CP star birth.