Fast rotating massive stars and the origin of the abundance patterns in galactic globular clusters

Abstract

Aims. We propose the Wind of Fast Rotating Massive Stars scenario to explain the origin of the abundance anomalies observed in globular clusters. Methods. We compute and present models of fast rotating stars with initial masses between 20 and 120 M for an initial metallicity Z = 0.0005 ([Fe/H] −1.5). We discuss the nucleosynthesis in the H-burning core of these objects and present the chemical composition of their ejecta. We consider the impact of uncertainties in the relevant nuclear reaction rates. Results. Fast rotating stars reach critical velocity at the beginning of their evolution and remain near the critical limit during the rest of the main sequence and part of the He-burning phase. As a consequence they lose large amounts of material through a mechanical wind which probably leads to the formation of a slow outflowing disk. The material in this slow wind is enriched in H-burning products and presents abundance patterns similar to the chemical anomalies observed in globular cluster stars. In particular, the C, N, O, Na and Li variations are well reproduced by our model. However the rate of the 24 Mg(p, γ) has to be increased by a factor 1000 around 50 × 10 6 K in order to reproduce the amplitude of the observed Mg-Al anticorrelation. We discuss how the long-lived low-mass stars currently observed in globular clusters could have formed out of the slow wind material ejected by massive stars.

Stellar populations in ω Centauri: a multivariate analysis

“…The Na-O anticorrelation is generally attributed to pollution from H-burning at high temperature, in either fast rotating massive stars (Decressin et al 2007) (2003) attribute the increasing La/Eu in ω Centauri to pollution by AGB stars after gas removal by supernovae of type II (hereafter SN II) at the end of a first episode of star formation. We note however that these two groups have the same O abundance as OC1, and that they are not markedly He-enriched, indicating that they formed from gas that was not much polluted.…”

Globular cluster formation with multiple stellar populations from hierarchical star cluster complexes

“…In this scenario, chemical abundances between the two generations are different because chemical abundances of gas ejected from fast-rotating massive stars (e.g., Decressin et al 2007), supermassive stars (e.g., Denissenkov & Hartwick 2014), massive interacting binaries (e.g., Bastian et al 2013), and AGB stars (e.g.,D08) are quite different from the averaged ones of FG stars. This scenario has been suggested to have a number of serious problems in explaining the fundamental properties of GCs, for example, the larger fraction of SG stars in GCs with multiple stellar populations.…”

CNO abundances in the globular clusters NGC 1851 and NGC 6752★

“…The astrophysical site in which these nuclear reactions occur continues to be debated with asymptotic giant branch (AGB) stars, fast rotating massive stars, massive binaries and supermassive stars among the candidates (Fenner et al 2004;Ventura & D'Antona 2005;Karakas et al 2006;Decressin et al 2007b;de Mink et al 2009;Marcolini et al 2009;Denissenkov & Hartwick 2014). Additionally, many details regarding the production of these abundance variations including the initial mass function, minimum timescale, required mass budget, degree of (or need for) dilution with pristine gas and star formation modes still need to be established (Bastian et al 2013;Renzini 2013).…”