CARINI, RobertaRobertaCARINIBROCATO, EnzoEnzoBROCATORAIMONDO, GabriellaGabriellaRAIMONDOMARCONI, MarcellaMarcellaMARCONI2021-02-012021-02-0120170035-8711http://hdl.handle.net/20.500.12386/30135This work analyses the effect of the Helium content on synthetic Period-Luminosity Relations (PLRs) and Period-Wesenheit Relations (PWRs) of Cepheids and the systematic uncertainties on the derived distances that a hidden population of He-enhanced Cepheids may generate. We use new stellar and pulsation models to build a homogeneous and consistent framework to derive the Cepheid features. The Cepheid populations expected in synthetic color-magnitude diagrams of young stellar systems (from 20 Myr to 250 Myr) are computed in several photometric bands for Y = 0.25 and Y = 0.35, at a fixed metallicity (Z = 0.008). The PLRs appear to be very similar in the two cases, with negligible effects (few %) on distances, while PWRs differ somewhat, with systematic uncertainties in deriving distances as high as about 7% at log P < 1.5. Statistical effects due to the number of variables used to determine the relations contribute to a distance systematic error of the order of few percent, with values decreasing from optical to near-infrared bands. The empirical PWRs derived from multi-wavelength datasets for the Large Magellanic Cloud (LMC) is in a very good agreement with our theoretical PWRs obtained with a standard He content, supporting the evidence that LMC Cepheids do not show any He effect.STAMPAenArticle10.1093/mnras/stx9272-s2.0-85079691174000406629100020http://arxiv.org/abs/1704.08875v1https://academic.oup.com/mnras/article/469/2/1532/37474922017MNRAS.469.1532CFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering