Joint Astrophysical Colloquium
Metallicity dependence of Classical Cepheids Period-Luminosity relations and the extragalactic distance scale.
Vincenzo Ripepi (INAF-OACN)
Thursday 08/02/2024 @ 11:30, Sala Antonio Sollima (IV piano Battiferro)
Classical Cepheids (DCEPs) are the most important primary indicators of the extragalactic distance scale thanks to the tight Period-Luminosity relations that held for these starsHowever, despite many observational and theoretical efforts during the past years, there is still no general consensus on the detailedcalibration of such PL relations, especially for what concerns their dependence on metallicity. In this context, we started the project: "Cepheid metallicity in the Leavitt law" (C-MetaLL) with the immediate goal of obtaining homogeneous high-resolution spectroscopy and near-infrared time-series photometry for a sample of about 350 DCEPs, thus increasing by more than 50% the number of pulsators with this kind of data, and extending significantly the DCEP sample towards the metal-poor regime. We used these data in combination with Gaia parallaxes to determine metallicity-dependent PL relations for a variety of photometric bands. We find a large negative coefficient of the metallicity term (the so-called gamma coefficient) for all the PL relations investigated so far, with no variation as a function of wavelength. The typical values of the inferred gamma are around -0.4:-0.5 mag/dex, larger than most of the recent determinations present in the literature. The consequences for the calibration of the extra-galactic distance scale are discussed.