Open AccessKappa‐mechanism excitation of retrograde mixed modes in rotating B‐type stars
Author(s) -
Townsend R. H. D.
Publication year - 2005
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2005.09585.x
Subject(s) - physics , stars , instability , astrophysics , adiabatic process , rotation (mathematics) , stellar rotation , mechanics , geometry , quantum mechanics , mathematics
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 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, as a result of the same iron‐bump opacity mechanism that is usually associated with SPB and β Cep stars. At one‐half of the critical rotation rate, the instability for the modes with azimuthal orders m = 1 to 4 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.