Townsend, Richard Henry Denny; (1997) Non-radial pulsation of early-type stars. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

A comprehensive study of pulsation in early-type (O and B) stars is undertaken. Starting with the equations of hydrodynamics, expressions governing adiabatic, non-radial pulsation in such stars are derived, along with complementary formulations of the boundary conditions suitable for solution of the equations. Two types of structure models are presented, one simplistic and the other more physically realistic, and a discussion of various techniques currently used for solution of the pulsation equations is applied to the latter type of models. Such solution demonstrates that early-type main-sequence stars can be expected to be vibrationally unstable towards an opacity-driven excitation mechanism; furthermore, a consideration of the boundary conditions in such stars shows that some types of pulsation will be associated with trans-photospheric wave leakage through the stellar surface, possibly accounting for the wind variability observed in these systems. The interaction between rotation and pulsation is investigated in some depth, with a discussion of two different techniques for approaching the problem. It is demonstrated that rotation leads to the introduction of both convective and quasi-toroidal pulsation, and, furthermore, that it will serve to confine pulsation activity towards equatorial regions. The emphasis throughout the discussion is placed on the numerical implementation of current theories. All theoretical developments are combined in a pair of computer codes which model the line-profile variations of stars undergoing non-radial pulsation. The implementation of these models is discussed, with particular emphasis on the spectral-synthesis approach adopted, and they are compared with similar codes developed by other authors. The models are used to investigate some basic aspects of line-profile variability, with a discussion of the mechanisms behind the phenomenon, and a consideration of a number of issues which have previously been overlooked in the field; in particular, the possibility that a star may exhibit line-profile variability, but no ostensible photometric variability, is demonstrated, and the observational consequences of the trans-photospheric wave leakage previously mentioned are examined.

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