2025/08/24 by Ripepi, V., Trentin, E., Catanzaro, G. +8 · 1 citation
#Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Solar and Stellar Astrophysics (astro-ph.SR)
paper · doi:10.48550/arxiv.2508.17447
The C-MetaLL project has provided homogeneous spectroscopic abundances of 290 Classical Cepheids (DCEPs) for which we have the intensity-averaged magnitudes in multiple optical and near-infrared (NIR) bands, periods, pulsation modes, and Gaia parallaxes. Our goal is to derive updated period-Wesenheit-metallicity (PWZ) relations using the largest and most homogeneous metallicity sample ever used for such analyses, covering a range of -1.3<[Fe/H]<+0.3 dex. We computed several optical and NIR Wesenheit magnitudes using 275 DCEPs with reliable parallaxes, by applying a robust photometric parallax technique, which simultaneously fits all parameters -- including the global Gaia parallax counter-correction -- and handles outliers without data rejection. We find a stronger metallicity dependence (γ≈ -0.5 mag/dex in optical, -0.4 mag/dex in NIR) than recent literature reports. Gaia parallax zero-point conter-corrections (ε) vary smoothly across bands, with an average value of ∼10 μas, aligning with previous determinations. Applying our PWZ relations to LMC Cepheids yields distances generally consistent within 1σ with geometric estimates. The choice of reddening law has a negligible impact, while using only fundamental-mode pulsators significantly increases the uncertainties. Including α-element corrections increases |γ| and reduces ε. However, we find statistically consistent γ values with the literature, particularly for the key Wesenheit magnitude in the HST bands, by restricting the sample to the brighter (i.e. closer) objects, or by including only pulsators with -0.7<[Fe/H]<0.2 dex. Our results hint at a large γ or a non-linear dependence on metallicity of DCEP luminosities at the metal-poor end, which is difficult to quantify with the precision of parallaxes of the present dataset.