Atmospheric Dynamics in a Model RR Lyrae Star

Citation

Castor, John Irvin (1967) Atmospheric Dynamics in a Model RR Lyrae Star. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/EKJM-HV30. https://resolver.caltech.edu/CaltechETD:etd-05082008-142946

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. A dynamical model of an RR Lyrae star has been constructed which is similar to those of Christy (1) in its treatment of the envelope interior to the hydrogen ionization zone but which describes the hydrogen ionization zone and the outer atmosphere in some detail. In the optically thin region heat transfer is described with the gray equation of radiation transfer which yields an integral expression for the heating rate, assuming small deviations from sphericity. The model which has been constructed has the parameters: M[subscript bol] = .76, T[subscript e] = 6500°K, [...] = .58[...], Y = .30. The model results of Christy for the same parameters have been used as initial conditions. The results have indicated a close connection between the complex hydrogen ionization zone dynamics and the observable phenomena in the star, such as rising branch shocks and the shape of the velocity curve during the decreasing light phase. The work done by the hydrogen ionization zone to maintain pulsation has been found in this calculation to be in excellent agreement with the figure obtained by Christy for this star. Deviations from radiative equilibrium in the optically thin layers have been found to be confined to tau less than 0.1 and to high gravity, low temperature phases, when they may exceed 500° K. Model atmospheres have been constructed with the dynamical pressure and temperature distributions using Mihalas' program (2). The emergent continuum fluxes obtained show considerable similarity to observed monochromatic light variation, although the amplitudes are greater and the rise time is less than is observed. The errors in temperature determinations based on fitting equilibrium models to the continuum have been found to be of the same order as fluctuations which appear in observational determinations of the radius variation. It has been concluded that the differences between the model and the observed stars may be due in part to the omission of convection from the model, since it may become quite important during high gravity phases.

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