Physics & Astronomy ETDs

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Models for thirteen classical Cepheids found in galactic clusters or associations are analyzed. The models are calculated using the most recently published photometric data and theoretical evolutionary tracks. The linearized equations of mass, momentum and energy conservation are solved subject to an infinitesimal radial perturbation of each equilibrium model. The equations are first solved in the adiabatic approximation. This solution is then used as the initial value for the iterative solution of the non-adiabatic equations. The linearized analysis provides information on pulsation periods of fundamental and harmonic modes, stability against pulsations and phase differences between various physical parameters, such as radius, luminosity and velocity. The results of the analysis are compared with observed quantities. Preliminary comparison reveals that observational data, evolutionary calculations and pulsational stability calculations are not entirely consistent. The periods calculated do not agree with the observed periods in the sense that they are smaller than observed. Two methods of modifying the input parameters to match the calculated and observed periods are followed. In the first the mass is reduced until the periods match. The required masses are an average of 66 percent of the masses predicted by evolutionary calculations and some are as much as 50 percent smaller. This much reduction is not compatible with present evolutionary calculations and might imply that such calculations must account for considerable mass loss prior to the Cepheid phase. The second method is to modify the effective temperature until the calculated periods match the observed. The period is a much stronger function of the temperature than of the mass and only a relatively small reduction in temperature is necessary. The average being 450 degrees Kelvin. In some cases the required temperatures were within the range determined from observational data of several authors. The minimum temperature change was 100 degrees K and the maximum was 700 degrees K. The implications of these models are discussed.

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Level of Degree


Department Name

Physics & Astronomy

First Committee Member (Chair)

David Solomon King

Second Committee Member

Christopher Pratt Leavitt

Third Committee Member

Victor H. Regener



Document Type