The diffusion of gallium in main-sequence peculiar stars.

Abstract

New observations of the gallium abundance in main-sequence peculiar stars are now available in the literature. The present paper analyses these new data in the framework of the diffusion processes. The radiative accelerations of gallium are computed, with up-to-date gallium line data, in various physical conditions of stable main-sequence star atmospheres. Zero mass loss is assumed. The role of the 1400 A absorption feature, attributed to Si II autoionization, is investigated and appears of minor importance. The main observed trends (the anti-correlation between the gallium and silicon overabundances in Ap stars and the smaller gallium enhancement for lower effective temperature) may be explained by the calculations on the gallium diffusion presented here. It is proposed here that the presence of a magnetic field modifies strongly the gallium accumulation.