Massive binaries and the enrichment of the interstellar medium in globular clusters

Abstract

Abstract. Abundance anomalies observed in globular cluster stars indicate pollution with material processed by hydrogen burning. Two main sources have been suggested: asymptotic giant branch (AGB) stars and massive stars rotating near the break-up limit (spin stars). We discuss the idea that massive binaries may provide an interesting alternative source of processed material. We discuss observational evidence for mass shedding from interacting binaries. In contrast to the fast, radiatively driven winds of massive stars, this material is typically ejected with low velocity. We expect that it remains inside the potential well of a globular cluster and becomes available for the formation or pollution of a second generation of stars. We estimate that the amount of processed low-velocity material that can be ejected by massive binaries is larger than the contribution of the two previously suggested sources combined.

Investigating a predicted metallicity [Fe/H] variation in the Type II Globular Cluster NGC 362

“…The GC potential well is able to retain this gas and eventually leads to the subsequent formation of chemically enriched stars (D'Ercole et al 2008). Several mechanisms and polluter candidates have been proposed as responsible for the observed nucleosynthesis in GCs, such as intermediate-mass (∼4-8M ) asymptotic giant branch (AGB) stars (Ventura et al 2001;D'Antona et al 2016), fast rotating massive main sequence (MS) stars (Meynet et al 2006;Decressin et al 2007), interacting massive binaries (de Mink et al 2009), supermassive (M>10 4 M ) stars (Denissenkov & Hartwick 2014), and the accretion model (Bastian et al 2013). However, the possible polluters cannot be fully established yet and no current scenario is able to completely reproduce the complex behavior of MSPs (Renzini et al 2015).…”

Chemical study of the metal-rich globular cluster NGC 5927

“…Na-poorer O-rich) polluted the intra-cluster gas left behind with processed material and then a second generation (SG) of stars was formed being Na-richer and O-pooer (Caloi & D'Antona 2011). There are several candidates for this light element polluter: intermediate mass AGB stars (D'Antona et al 2002), fast rotating massive MS stars (Decressin et al 2007) and massive binaries (de Mink et al 2009). On the other hand, heavy elements are produced by neutron capture.…”

Light-element abundance variations in the Milky Way halo

“…This abundance bimodality has been studied extensively in globular clusters (Langer et al 1992;Kraft 1994;and Gratton et al 2004 all provide thorough reviews of the topic), and explanations for the second abundance subgroup have varied from pollution (Cannon et al 1998) to internal mixing (Langer 1985) to enrichment of star-forming gas by moderate-to high-mass stars (e.g., Cottrell & DaCosta 1981;Yong et al 2008) or high-mass binaries (de Mink et al 2010). Surface pollution of already-formed stars would result in abundance anomalies that are erased at first dredge-up, while current models of deep mixing (e.g., Charbonnel & Zahn 2007) indicate that it only begins to operate after first dredge-up.…”

“…In the primordial enrichment scenario, there is ongoing discussion over the exact source of enriching material. In some models the source is moderately high-mass (∼4−5 M ) AGB stars (e.g., Parmentier et al 1999), while Decressin et al (2007) claim that rotating high-mass (M > ∼ 10 M ) stars are a better source for processed material because of their very short lifetimes and de Mink et al (2010) prefer highmass binaries because of their potentially strong mass loss and low wind velocities.…”