Silicon absorption in UV spectra of AP SI stars.

Abstract

The authors investigate the role of silicon UV absorption occurring in the atmosphere of early-type stars. A detailed analysis of the λλ1250 - 1850 Å range is presented. High-resolution spectra are obtained from the IUE database for typical silicon stars and for a few normal main-sequence stars. The strongest absorption in these spectra are the resonance lines of Si II, and three large features (λ1400, λ1560 and λ1770 Å) which are strongly enhanced in the spectra of ApSi stars. For the hottest silicon stars, a discontinuity at 1310 Å is observed. The atomic data are carefully reviewed for Si II to perform spectrum synthesis calculations showing out more precisely the silicon absorption.