The effect of intermediate-mass close binaries on the chemical evolution of globular clusters

Abstract

Context. The chemical processes during the asymptotic giant branch (AGB) evolution of intermediate-mass single stars predict most of the observations of the different populations in globular clusters although some important questions still need to be further clarified. In particular, to reproduce the observed anticorrelations of Na-O and Al-Mg, chemically enriched gas lost during the AGB phase of intermediate-mass single stars must be mixed with matter with a pristine chemical composition. The source of this matter is still debated. Furthermore, observations reveal that a significant fraction of the intermediate-mass and massive stars are born as components of close binaries. Aims. We investigate the effects of binaries on the chemical evolution of globular clusters and on the origin of matter with a pristine chemical composition that is needed for the single-star AGB scenario to work. Methods. We used a population synthesis code that accounts for binary physics to estimate the amount and the composition of the matter returned to the interstellar medium of a population of binaries. Results. We demonstrate that the mass lost by a significant population of intermediate-mass close binaries in combination with the single-star AGB pollution scenario may help to explain the chemical properties of the different populations of stars in globular clusters.

Massive double compact object mergers: gravitational wave sources and r-process element production sites

“…When we present simulations with β < 1 the latter value refers to the amount of mass lost by the loser and accreted by the gainer in case Br binaries. Note that with our merger criterion (DDV04, Vanbeveren et al 2012) ∼20−30% of all case A binaries merge. The percentage of case Br mergers depends on the assumed value of β (see also Vanbeveren et al 2013) and this will obviously affect the predicted population of double compact star binaries.…”

“…A recent summary was given in Vanbeveren et al (2012). Although the latter paper deals with intermediate mass binaries, as far as the RLOF is concerned the majority of these basic ingredients remain valid also for massive stars and are not repeated here.…”

The double sub-giant branch of NGC 6656 (M 22): a chemical characterization

“…The accepted cluster evolutionary scenario is that normal GCs have been polluted with hot H-burning products by first-generation asymptotic giant branch stars (AGB, Ventura et al 2001;D'Antona & Caloi 2004), and/or fast rotating massive stars (Decressin et al 2007). Massive binaries have also been proposed as an alternative source (de Mink et al 2009;Vanbeveren et al 2011). Stars formed as secondgeneration members were born from the material released by these proposed first-generation polluters.…”

Blue supergiant progenitor models of type II supernovae

“…secondary), A is the binary separation, i and f stand for initial and final values, R Roche is the Roche radius of the primary, λ is determined by the density structure of the primary's outer atmosphere and on its internal energy that can help to expel the common envelope (see Dewi & Tauris 2000, for a detailed description and computation), and α describes the efficiency of the energy conversion. Similarly as in Vanbeveren et al (2012), we present population synthesis computations for αλ = 0.2, 0.5 and 1. An attractive alternative is the model where matter escapes from the system via the second Lagrangian point L 2 from where it forms a circumbinary disk (van den Heuvel 1993).…”

“…When at least one of the equilibrium radii is larger than the corresponding Roche radius, we conclude that the system merged. For merging systems our population code calculates the matter lost through the non-conservative Roche-lobe overflow up to that moment (see also Vanbeveren et al 2012).…”