Cepheids PL relation metallicity dependence

We find a large negative metallicity effect on the intercept ({gamma} coefficient) of all the PL and PW relations investigated in this work, while present data still do not allow us to draw firm conclusions regarding the metal dependence of the slope ({delta} coefficient). The typical values of {gamma} are around -0.4:-0.5mag/dex, which is larger than most of the recent determinations present in the literature. We carried out several tests, which confirm the robustness of our results.

As in our previous works, we find that the inclusion of a global zero point offset of Gaia parallaxes provides smaller values of {gamma} (in an absolute sense). However, the assumption of the geometric distance of the Large Magellanic Cloud (LMC) seems to indicate that larger values of {gamma} (in an absolute sense) would be preferred.