The (gamma) Doradus stars are a newly-discovered class of gravity-mode pulsators which lie just at or beyond the red edge of the (delta) Scuti instability strip. We present the results of calculations which predict pulsation instability of high-order g-modes with periods between 0.4 and 3 days, as observed in these stars. The pulsations are driven by the modulation of radiative flux by convection at the base of a deep envelope convection zone. Pulsation instability is predicted only for models with temperatures at the convection zone base between (approximately)200,000 and (approximately)480,000 K. The estimated shear dissipation due to turbulent viscosity within the convection zone, or in an overshoot region below the convection zone, can be comparable to or even exceed the predicted driving, and is likely to reduce the number of unstable modes, or possibly to quench the instability. Additional refinements in the pulsation modeling are required to determine the outcome. A few Doradus stars have been observed that also pulsate in (delta) Scuti-type p-modes, and at least two others have been identified as chemically peculiar. Since our calculated driving region is relatively deep, Doradus pulsations are not necessarily incompatible with surface abundance peculiarities or with (delta) Scuti p-mode pulsations driven by the H and He-ionization (kappa) effect. Such stars will provide useful observational constraints on the proposed Doradus pulsation mechanism.
PDF
download
878987797
028-85220240
