Uncertainties in the chemical composition of B-type stars: effects on the opacity and on the excitation of pulsation modes

Recent determinations of element abundances in early-B stars have shown a significant discrepancy with those derived for the Sun. β Cep pulsators are early-B stars whose pulsations are driven by the opacity mechanism operating at the Fe-group opacity bump (e.g. Dziembowski & Pamyatnykh 1993). Since each element contributes differently to the stellar opacity in the Z-bump region, differences in the metal mixture may affect the pulsation properties of these early-B stars. Here we study the role of different elements in the stellar opacity of B-type stars, and the consequences of the uncertainties in the composition of the metal mixture for the instability strip of β~Cep stars.