Rapidly rotating second-generation progenitors for the blue hook stars of {\omega} Cen

TL;DR

This paper investigates the origins of blue hook stars in 0 Cen, proposing that rapid rotation in second-generation progenitors leads to larger helium core masses, explaining their luminosity and prevalence.

Contribution

It introduces a model linking rapid rotation of progenitors to increased helium core mass, accounting for blue hook star properties in 0 Cen.

Findings

Helium core masses up to 0.04 solar masses larger are needed to explain luminosity.

Rotation dispersion among progenitors influences late-flash-mixing events.

Rapid rotation may be common in massive globular cluster second-generation stars.

Abstract

Horizontal Branch stars belong to an advanced stage in the evolution of the oldest stellar galactic population, occurring either as field halo stars or grouped in globular clusters. The discovery of multiple populations in these clusters, that were previously believed to have single populations gave rise to the currently accepted theory that the hottest horizontal branch members (the blue hook stars, which had late helium-core flash ignition, followed by deep mixing) are the progeny of a helium-rich "second generation" of stars. It is not known why such a supposedly rare event (a late flash followed by mixing) is so common that the blue hook of {\omega} Cen contains \sim 30% of horizontal branch stars 10 , or why the blue hook luminosity range in this massive cluster cannot be reproduced by models. Here we report that the presence of helium core masses up to \sim 0.04 solar masses larger than the core mass resulting from evolution is required to solve the luminosity range problem. We model this by taking into account the dispersion in rotation rates achieved by the progenitors, whose premain sequence accretion disc suffered an early disruption in the dense environment of the cluster's central regions where second-generation stars form. Rotation may also account for frequent late-flash-mixing events in massive globular clusters.