ETTORI, STEFANOSTEFANOETTORIGhirardini, V.V.GhirardiniEckert, D.D.Eckert2021-11-302021-11-3020200004-6337http://hdl.handle.net/20.500.12386/31193We present the constraints on the helium abundance in 12 X-ray luminous galaxy clusters that have been mapped in their X-ray and Sunyaev-Zeldovich (SZ) signals out to $R_{200}$ for the XMM-Newton Cluster Outskirts Project (X-COP). The unprecedented precision available for the estimate of $H_0$ allows us to investigate how much the reconstructed X-ray and SZ signals are consistent with the expected ratio $x$ between helium and proton densities of 0.08-0.1. We find that a $H_0$ around 70 km/s/Mpc is preferred from our measurements, with lower values of $H_0$ as requested from the Planck collaboration (67 km/s/Mpc) requiring a 34% higher value of $x$. On the other hand, higher values of $H_0$, as obtained by measurements in the local universe, impose $x$, from the primordial nucleosynthesis calculations and current solar abundances, reduced by 37--44\%.STAMPAenArticle10.1002/asna.2020237802-s2.0-85080980357WOS:000517466200001https://onlinelibrary.wiley.com/doi/10.1002/asna.202023780http://arxiv.org/abs/1911.05039v22020AN....341..210EFIS/05 - ASTRONOMIA E ASTROFISICA