On the Distance of Magellanic Clouds: First Overtone Cepheids

We present a detailed comparison between predicted and empirical PL I , K relations and the Wesenheit function for Galactic and Magellanic Cloud (MC) first overtone (FO) Cepheids. We find that zero points predicted by Galactic Cepheid models based on a noncanonical (mild overshooting) mass-luminosity ( ML ) relation are in very good agreement with empirical zero points based on Hipparcos parallaxes, while those based on the canonical (no overshooting) ML relation are ≈0.2-0.3 mag brighter. We also find that the predicted and empirical PL K relations and Wesenheit function give, according to optical ( V , I ; Optical Gravitational Lensing Experiment) and near-infrared ( K ; Two Micron All Sky Survey) data, mean distances to the MCs that agree at the 2% level. Individual distances to the Large and the Small MCs are 18.53 ± 0.08 and 19.04 ± 0.11 (theory) as well as 18.48 ± 0.13 and 19.01 ± 0.13 (empirical). Moreover, predicted and empirical FO relations do not present, within the errors, a metallicity dependence. Finally, we find that the upper limit in the FO period distribution is a robust observable to constrain the accuracy of pulsation models. Current models agree within 0.1 in log P with the observed FO upper limits.