Distribution of helium and silicon in the atmospheres of Bp stars HD168785 and HD21699

We present a study of stratification of helium and silicon in the atmospheres of CP stars HD 168785 (He-r) and HD 21699 (He-w). The distribution of these elements with depth is well described by the mechanism of diffusion under the effect of gravity, radiation pressure and stellar wind. We studied the stratification of these elements in different regions of the surface of HD 21699. We demonstrate that as the star rotates the abundance of He and Si changes in the antiphase. The position of the abundance maximum varies within small limits with optical depth as well.