Description
In dense stellar environments like globular clusters (GCs), dynamical interactions are expected to alter binary properties, potentially disrupting or hardening close binary systems. Despite these expectations, the detailed comparison of close binary fractions between field stars and GCs remains underexplored. In this talk, I will present an analysis of the close binary fraction in a carefully selected sample of field stars and 10 GCs using Gaia Radial Velocity Spectrometer (RVS) data - the largest sample of GCs analysed using multi-epoch spectroscopy to date. By assessing the peak-to-peak variations of the sources’ radial velocity (RV) and modelling their dependence on the Gaia RVS magnitude, we can estimate the close binary fractions through a method that fits the distribution as the product of two Gaussian distributions. Our results confirm previous estimates of the close binary fractions in GCs and extend the analysis to additional clusters. Despite matching stellar parameters between the field and GC samples, our findings reveal that GCs possess a significantly lower close binary fraction compared to field stars. Interestingly, we do not detect any trend of binary fraction with cluster metallicity – metal-rich and metal-poor GCs are uniformly binary-poor. I will discuss possible interpretations, including dynamical hardening in dense environments and the effects of common envelope evolution, which may lead to companion accretion or merger events.
