Classical Cepheids are the most important primary indicators for the extragalactic distance scale. Establishing the precise zero points of their Period-Luminosity and Period-Wesenheit (PL/PW) relations has profound consequences on the estimate of H0. Type II Cepheids are also important distance indicator and tracers of old stellar populations. The recent Data Release 2 (DR2) of the {\it Gaia} Spacecraft includes photometry and parallaxes for thousands of classical and type II cepheids. We aim at reviewing the classification of {\it Gaia} DR2 Cepheids and to derive precise PL/PW for Magellanic Cloud (MCs) and Galactic Cepheids. Information from the literature and the {\it Gaia} astrometry and photometry are adopted to assign DR2 Galactic Cepheids to the classes: Classical, Anomalous and Type II Cepheids. We re-classify the DR2 Galactic Cepheids and derive new precise PL/PW relations in the {\it Gaia} passbands for the MCs and Milky Way Cepheids. We investigated for the first time the dependence on metallicity of the PW relation for Classical Cepheids in the {\it Gaia} bands, finding non-conclusive results. According to our analysis, the zero point of the {\it Gaia} DR2 parallaxes as estimated from Classical and Type II Cepheids seems to be likely underestimated by ∼0.07 mas, in full agreement with recent literature. The next {\it Gaia} data releases are expected to fix this zero point offset to eventually allow a determination of H0 to less than 1\%.
@article{arxiv.1810.10486,
title = {A re-classification of Cepheids in the Gaia Data Release 2},
author = {V. Ripepi and R. Molinaro and I. Musella and M. Marconi and S. Leccia and L. Eyer},
journal= {arXiv preprint arXiv:1810.10486},
year = {2019}
}
Comments
Accepted on A\&A, 19 pages. New version after the refereeing process, including many improvements and new features. The electronic versions of Table 2, Table 5, Table 7 and Table 8 are available in the Ancillary Files repository