The IACOB project XIII. Helium enrichment in O-type stars as a tracer of past binary interaction

TL;DR

This study examines helium and nitrogen surface abundances in 180 Galactic O-type stars, finding that about 20% show patterns indicating past binary interactions, challenging single-star evolution models.

Contribution

It provides evidence that a significant fraction of massive stars' surface abundances are shaped by binary interactions, not just single-star evolution.

Findings

20% of stars show helium and nitrogen patterns unexplainable by single-star models

Majority of stars with helium enrichment are likely binary interaction products

Binary interactions significantly influence surface chemical compositions of massive stars

Abstract

There is increasing evidence that single-star evolutionary models are inadequate to reproduce all observational properties of massive stars. Binary interaction has emerged as a key factor in the evolution of a significant fraction of massive stars. In this study, we investigate the helium ($Y_{\mathrm He}$) and nitrogen ($\epsilon_{\mathrm N}$) surface abundances in a comprehensive sample of 180 Galactic O-type stars with projected rotational velocities $v\sin(i)\leq150{\mathrm km}\cdot{\mathrm s}^{-1}$. We found a subsample ($\sim20\%$ of the total, and $\sim80\%$ of the stars with $Y_{\mathrm He}\geq0.12$) with a $Y_{\mathrm He}$ and $\epsilon_{\mathrm N}$ combined pattern unexplainable by single-star evolution. We argue that the stars with anomalous surface abundance patterns are binary interaction products.