Astronomy and Astrophysics – Astrophysics
Scientific paper
2005-06-24
Mon.Not.Roy.Astron.Soc.364:573-582,2005
Astronomy and Astrophysics
Astrophysics
11 pages, 6 figures, accepted by MNRAS
Scientific paper
10.1111/j.1365-2966.2005.09585.x
I examine the stability of retrograde mixed modes in rotating B-type stars. These modes can be regarded as a hybrid between the Rossby modes that arise from conservation of vorticity, and the Poincare 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 $\beta$ 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 SPB and pulsating Be stars, and to 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.
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