On the distance of Magellanic Clouds: First overtone Cepheids

We present a detailed comparison between predicted and empirical relations and the Wesenheit function PLI,K 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 approximate to0.2-0.3 mag brighter. We also find that the predicted and empirical PLK 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 with the log P observed FO upper limits.