The Binary Populations of Stellar Streams are Set by Cluster Dynamics

TL;DR

This study uses N-body simulations to explore how cluster dynamics influence the binary star populations in stellar streams, revealing the effects of internal tides, encounters, and initial conditions on binary disruption and segregation.

Contribution

It provides the first detailed analysis of how in-cluster dynamical processes shape the binary populations in low-mass globular cluster streams.

Findings

Wide binaries are disrupted by tides and encounters.

Close binaries are concentrated at the stream center.

Binary fractions and segregation depend on initial cluster density.

Abstract

We present a suite of direct N-body simulations of low mass ($<10^4~M_{\odot}$) globular cluster streams initialized with observationally-motivated binary demographics in order to understand the effect of in-cluster dynamical processing on the stream binary population. The models are initialized with a range of stellar densities and cluster orbits, and Poisson variation in the number of massive and short-lived stars. Wide binaries are disrupted on short timescales by internal tides and on long timescales by two-body encounters. Tides are most important prior to impulsive mass loss-driven cluster expansion. Close binaries ($P_{\rm orb}<10^2~\rm yr$) are most abundant at the stream center due to cluster mass segregation. The wide binary fraction and the degree of binary segregation in the resulting stream are sensitive to the initial cluster density and massive star fraction. In mock radial velocity surveys of the simulated streams, undetectable binaries have velocity amplitudes of $\sim$$0.5$-$1~\rm km~s^{-1}$, adding $\sim0.1~\rm km\ s^{-1}$ of velocity dispersion to the streams, and are dynamically depleted by $\sim10$-$60\%$ compared to the initial binary population. Custom N-body models of Milky Way streams with binaries will allow a holistic understanding of their dynamical structures in advance of upcoming multi-epoch spectroscopic surveys.