Cepheid Envelope Models

Details Cepheid Envelope Models Cepheid Envelope Models

Jan 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993pasp..105..123m&link_type=abstract

Publications of the Astronomical Society of the Pacific, v.105, p.123

Astronomy and Astrophysics

Astronomy

Scientific paper

Models of Cepheid envelopes are constructed to examine their characteristics and compare them with observations. The models are initially in hydrostatis equilibrium and the mass-luminosity relations of different stellar-evolution calcuations can be assigned to groups of these models. Linear nonadiabatic pulsation analysis of the models provides an estimate of the period and expected pulsation mode. The pulsation mode depends on the period, with first-overtone pulsators expected for models with periods less than 10 days and fundamental-mode pulsators for longer periods. We find that those models with the higher luminosity for a given mass have characteristics similar to most binary and dynamical masses, and that empirical period-radius period-luminsotiy-temperature, and period-luminosity relations are found to correspond closest to the high-luminosity stellar-evolution calculations. A method for an explicit hydrodynamics and implicit radiative-transfer solution to the pulsational variation of the Cepheid models is described. This method is applied to the same series of models to obtain light and velocity curves. In most cases the pulsation characteristics of the models are similar to the results obtianed by the linear nonadiabatic analysis. Thus, the models that correspond to the highest-lumnosity stellar-evolution calculations give the best fit to empirical Cepheid relations. The phase lag between the minimum radius and the luminosity maximum is found to be dependent on temperature. The Fourier coefficients for the light and velocity curves are determined, and it is found that the light-curve coefficients have a greater scatter relative to the coefficients obtained from observed Cepheid light curves, while the theoretical velocity-curve coefficients are quite similar to those obtained from Cepheid observations. For those models that have bumps on the light curves, the bump Cepheid period-radius relation for these stars is very similar to that obtained from observed bump Cepheids. The same method of analysis described is also applied to a series of models that have opacities increased along the lines suggested by recent opacity calculations. In most cases the model characteristics are similar to those for the models described above. It is found that the models that best fit the empirical relations of Cepheids are those that correspond to the high-luminosity stellar-evolution calculations. (SECTION: Dissertation Abstracts)

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