Rapidly rotating second-generation progenitors for the `blue hook' stars of ω Centauri

Horizontal Branch (HB) stars belong to an advanced stage in the evolution of the oldest stellar galactic population, to be found in the halo, either diffused in the field or grouped in globular clusters. The recent discovery of the presence of multiple populations in these clusters, , previously believed “single population” systems, has helped to solve some of the problems related to the origin of the hottest HB members, which could be the progeny of a helium-rich “second generation”.. However, in a few massive GCs, in the colour magnitude diagram, the hottest HB stars occupy a region that standard stellar models faiil to reproduce. An especial challenge is the populated and well defined “blue hook” in ! Cen.. Here we show that its full reproduction requires, inter alia, stars with a spread in helium core masses.