Origin of the abundance patterns in Galactic globular clusters: constraints on dynamical and chemical properties of globular clusters

By T. Decressin, C. Charbonnel, G. Meynet. 2007

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Aims. We analyse the effects of a first generation of fast rotating massive stars on the dynamical and chemical properties of globular clusters. Methods. We use stellar models of fast rotating massive stars, losing mass through a slow mechanical equatorial winds to produce material rich in H-burning products. We propose that stars with high Na and low O abundances (hereafter anomalous stars) are formed from matter made of slow winds of individual massive stars and of interstellar matter. The proportion of slow wind and of interstellar material is fixed in order to reproduce the observed Li-Na anticorrelation in NGC 6752. Results. In the case that globular clusters, during their lifetime, did not lose any stars, we found that to reproduce the observed ratio of normal to anomalous stars, a flat initial mass function (IMF) is needed, with typically a slope x = 0.55 (a Salpeter’s IMF has x = 1.35). In the case that globular clusters suffer from an evaporation of normal stars, the IMF slope can be steeper: to have x = 1.35, about 96% of the normal stars would be lost. We make predictions for the distribution of stars as a function of their [O/Na] and obtain quite reasonable agreement with that one observed for NGC 6752. Predictions for the number fraction of stars with different values of helium, of the 12 C/ 13 Ca nd 16 O/ 17 O ratios are discussed, as well as the expected relations between values of [O/Na] and those of helium, of [C/N], of 12 C/ 13 C and of 16 O/ 17 O. Future observations might test these predictions. We also provide predictions for the present day mass of the clusters expressed in units of mass of the gas used to form stars, and for the way the present day mass is distributed between the first and second generation of stars and the stellar remnants.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/4058fc2eb34d61b2db41d01c09889c95f886ddc9

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Citations in the corpus

Origin of multiple stellar populations in globular clusters and their helium enrichment (2008, methodology): “Thus, I take the FRMS scenario as described in Decressin et al. (2007) at face value.”
Signatures of intrinsic Li depletion and Li-Na anti-correlation in the metal-poor globular cluster NGC 6397 , (2009, methodology): “…of the self-enrichment scenario the Li content of globular-cluster stars is actually an important tool to quantify the dilution factor between the ejecta of the massive stars responsible for pollution and the pristine intracluster matter (Prantzos & Charbonnel 2006; Decressin et al. 2007b,a).”
Formation and dynamical evolution of multiple stellar generations in globular clusters (2008, methodology): “…Prantzos & Charbonnel 2006; D’Antona et al. 2007; Decressin et al. 2007b), or the system evolves at constant mass and the IMF is highly anomalous (D’Antona & Caloi 2004; Decressin et al. 2007b, see also Downing & Sills (2007) for a dynamical study) and contains a significant number of FG polluters.”
Massive binaries as the source of abundance anomalies in globular clusters (2009, methodology): “The average composition of the ejecta are comparable to the yields of a 60 M⊙ spin star model computed by Decressin et al. (2007b) by adopting the same set of reaction rates.”
Multiple populations in globular clusters (2012, methodology): “…the total mass of AGB ejecta in a globular cluster is only 1-10% of the total globular cluster mass (Bekki & Norris 2006); similarly, if slow wind from FRMS stars is used to accumulate polluted mass, this provides only about 10% of the total number of low-mass stars (Decressin et al. 2007b).”
The evolution of runaway stellar collision products (2009, background): “Current scenarios that attempt to explain these chemical anomalies require pollution of the interstellar medium by massive stars (Decressin et al. 2007) or AGB stars (e.g. D’Ercole et al. 2008) in the central regions of the cluster and a second episode of star formation, followed by the loss of…”