¹ Bartol Research Institute, University of Delaware, Newark, DE 19711, USA
² Department of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT, UK

I examine the stability of retrograde mixed modes in rotating B-type stars. These modes can be regarded as a hybridization between the Rossby modes that arise from conservation of vorticity, and the Poincaré modes that are gravity waves modified by the Coriolis force. Using a non-adiabatic pulsation code based around the traditional approximation, I find that the modes are unstable in mid- to late-B type stars, due to the same iron-bump opacity mechanism usually associated with SPB and  Cep stars. At one half of the critical rotation rate, the instability for m=1...4 modes spans the spectral types B4 to A0. Inertial-frame periods of the unstable modes range from 100 days down to a fraction of a day, while normalized growth rates can reach in excess of 10^-5.

I discuss the relevance of these findings to the mass-loss mechanism of Be stars, and to the pulsation of the putative Maia class of variable star. I also outline some of the questions raised by this discovery of a wholly-new class of pulsational instability in early-type stars.

Submitted to MNRAS
Preprints from rhdt@bartol.udel.edu
Or on the web at http://www.star.ucl.ac.uk/~rhdt/publications/