Pulsational Instability of Cepheid Models.

Abstract

view Abstract Citations (3) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Pulsational Instability of Cepheid Models. Baker, Norman H. Abstract Models of classical Cepheids have been constructed by numerically integrating the linearized equations for radial oscillations. Equilibrium model envelopes which include about 40% of the mass of the star are first obtained. Convection is taken into account in the equilibrium models, but is assumed to have no interaction with the pulsations. For each model the appropriate period and the stability coefficient are determined. By constructing a series of models of gradually increasing mean radius, all having the same mass and mean luminosity, the mean radius corresponding to maximum instability is found. If several such series are made, each series having a different mass and corresponding luminosity, the instability region 33 in the effective temperature-luminosity diagram can be outlined and the period-luminosity relation determined. It is found that the ionization zone of hydrogen and both ionization zones of helium all contribute to the instability. The mean effective temperature at which maximum instability occurs depends only very weakly on mass and mean luminosity. The instability region is thus an almost vertical strip in the temperature-luminosity diagram. The width of this strip is in good agreement with the width of the observed Cepheid band, but the mean effective temperature at the center of the strip is several hundred degrees lower than that determined from observations (Kraft, R. P., Astrophys. J. 134, 616, 1961). This conclusion appears to be nearly independent of the assumed mass-luminosity law and of the assumed chemical composition. The calculated periods are rather larger than the observed ones, but depend upon the adopted masses. The slope of the period-luminosity relation, Mv = A - B logP, is somewhat larger (~30%) than the observed slope, but this result also depends upon the mass-lu minosity law. The period-luminosity relation also depends upon the assumed composition. Detailed results are presented and compared with the observations. Publication: The Astronomical Journal Pub Date: October 1963 DOI: 10.1086/109004 Bibcode: 1963AJ.....68..533B full text sources ADS |