Improving the Mass Determination of Galactic Cepheids

Abstract

We have selected a sample of Galactic Cepheids for which accurate estimates of radii, distances, and photometric parameters are available. The comparison between their pulsation masses, based on new period-mass-radius (PMR) relations, and their evolutionary masses, based on both optical and NIR color-magnitude (CM) diagrams, suggests that pulsation masses are on average of the order of 10% smaller than the evolutionary masses. Current pulsation masses show, at Ðxed radius, a strongly reduced dispersion when compared with values published in the literature. The increased precision in the pulsation masses is due to the fact that our predicted PMR relations based on nonlinear, convective Cepheid models present smaller standard deviations than PMR relations based on linear models. At the same time, the empirical radii of our Cepheid sample are typically accurate at the 5% level. Our evolutionary mass determinations are based on stellar models constructed by neglecting the e †ect of mass loss during the He burning phase. Therefore, the di †erence between pulsation and evolutionary masses could be intrinsic and does not necessarily imply a problem with either evolutionary and/or nonlinear pulsation models. The marginal evidence of a trend in the di †erence between evolutionary and pulsation masses when moving from short-to long-period Cepheids is also brieÑy discussed. The main Ðnding of our investigation is that the long-standing Cepheid mass discrepancy seems now resolved at the 10% level either if we account for canonical or mild convective core overshooting evolutionary models.