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Carson, T.R., and R.B. Stothers, 1988: Classical bump Cepheids: Reconciliation of theory with observations. Astrophys. J., 328, 196-206, doi:10.1086/166281.
New models of classical bump Cepheids lying along the Cepheid ridge line in the H-R diagram have been computed to obtain a more accurate set of predicted surface velocity curves. Statistical properties of these velocity curves and of the models' fundamental parameters are compared with published Cepheid observations of the highest available quality. Assuming the validity of the adopted opacities for the main pulsating stars, acceptable Cepheid models are found to be 0.5 mag brighter at a fixed stellar mass than standard evolutionary models. By accepting the implied luminosity increase, all the previously obtained manifestations of the Cepheid mass discrepancy—with the exception of the anomalous double-mode Cepheid masses—are resolved, at least in a statistical sense. Newly published orbital masses of individual Cepheids in binary systems are similarly compatible with the new pulsational masses.
The need for a luminosity increase of 0.5 mag has been independently inferred from standard evolutionary models of intermediate-mass and high-mass giant and supergiant stars from their location in the observational H-R diagram. A 0.5 mag increase is also fully consistent with the most recent evolutionary tracks including convective core overshooting, although it can be achieved by changing the initial chemical composition. This degree of interagreement implies that the traditionally accepted zero point of observed Cepheid luminosities is correct.
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