Comparison of observed vertical stratifications of iron in blue horizontal-branch stars to those predicted by atomic diffusion

ABSTRACT Recent spectroscopic analysis has shown that hot blue horizontal-branch (BHB) stars often exhibit a significant increase in iron abundance with depth in their atmospheres. The aim of this work is to verify whether these abundance stratifications are compatible with those that are predicted by atomic diffusion. Indeed, this physical process has been suspected for several decades of being at the origin of the abundance anomalies detected in BHB stars, as well as the observed photometric anomalies. Using the most recent version of the caratmotion code for modelling time-dependent diffusion in stellar atmospheres, we have calculated iron diffusion in the atmosphere of three BHB stars where iron stratification has been detected. It appears that the Fe stratifications predicted by our calculations are generally compatible with those observed. It is also shown that at certain phases detailed quantitative agreement between observations and calculations is achieved.