Massive interacting binaries as an enrichment source for multiple populations in star clusters

TL;DR

Massive interacting binaries can significantly contribute to the chemical enrichment of star clusters, providing the necessary material to explain multiple stellar populations through their ejecta enriched in specific elements.

Contribution

This study introduces detailed binary evolution models showing that massive binaries produce enriched ejecta matching observed abundance patterns in star clusters.

Findings

Binary ejecta are enriched in helium, nitrogen, sodium, and aluminum.

Approximately 25% of the binary system mass is returned as enriched material.

Enrichment occurs over about 12 million years, aligning with cluster formation timescales.

Abstract

We present a suite of binary evolution models with massive primaries (10 $\leq$ M$_1$ $\leq$ 40 M$_\odot$) and periods and mass ratios chosen such that the systems undergo non-conservative mass transfer while the primaries have helium cores. We track the total mass and chemical composition of the ejecta from these systems. This material shows the abundance signatures of hot hydrogen burning which are needed to explain the abundance patterns seen in multiple populations in massive star clusters. We then calculate the total yield of a population of binary stars with masses, mass ratios, and periods consistent with their distribution in a field population. We show that the overall abundance of this material is enriched in helium, nitrogen, sodium, and aluminum, and depleted in carbon, oxygen, and magnesium, by amounts that are consistent with observations. We also show that such a population of binaries will return approximately 25% of its mass in this ejecta (compared to 4% if all the stars were single), over a characteristic timescale of about 12 Myr. We argue that massive binaries must be seriously considered as a contributor to the source of enriched material needed to explain the multiple populations in massive clusters, since essentially all massive stars are formed in binaries or higher order multiples, massive binaries are primarily formed in clusters, and massive binaries naturally produce material of the right composition.