New Results on Pulsating OB Stars

Until very recently the physical mechanism driving oscillations in $\beta$~Cep and other early type stars has been a mystery. The breakthrough came with the publication of new OPAL and OP opacity data. Model calculations with the new opacities have demonstrated that the pulsations are driven by the familiar $\kappa$-mechanism, acting in the metal opacity bump at $T \approx 2 \times 10^5$K. The mechanism excites the low order $p$- and $g$-modes in the upper part of the instability strip and the high order $g$-modes in the lower part of the strip. The theoretical instability domains agree well with the observed domains of the $\beta$~Cep and the SPB stars. In this review I present these recent theoretical results and discuss their consequences for our understanding of B stars pulsations.