2010MNRAS.407.1767K

The aim of this study is to search for observational evidence of vertical iron stratification in the atmosphere of 14 blue horizontal-branch (BHB) stars. We have found from our numerical simulations that five BHB stars: B22, B186 in the globular cluster NGC288, WF2-820, WF2-2692 in M13 and B203 in M15 show clear signatures of the vertical stratification of iron whose abundance increases toward the lower atmosphere. Two other BHB stars (B334 in M15 and B176 in M92) also show possible iron stratification in their atmosphere. A dependence of the slope of iron stratification on the effective temperature was also discovered. It is found that the vertical stratification of iron is strongest in BHB stars with T_eff around 11500K. The slope of iron abundance decreases as T_eff increases and becomes negligible for the BHB stars with T_eff~ 14000K. These results support the hypothesis regarding the efficiency of atomic diffusion in the stellar atmospheres of BHB stars with T_eff{sce} 11500K.