Tracing the Origins of Mass Segregation in M35: Evidence for Primordially Segregated Binaries

TL;DR

This study uses Gaia DR3, Pan-STARRS, and 2MASS data with Bayesian analysis to investigate mass segregation in the young open cluster M35, revealing that binaries are more centrally concentrated and likely formed with a primordially segregated distribution.

Contribution

It provides the first detailed binary demographics extending to faint magnitudes and larger radii, demonstrating primordial segregation of binaries in M35.

Findings

Binary stars are more centrally concentrated than single stars.

Strong evidence for mass segregation within the binary population.

Binaries may have formed with a primordially segregated spatial distribution.

Abstract

M35 is a young open cluster and home to an extensive binary population. Using Gaia DR3, Pan-STARRS, and 2MASS photometry with the Bayesian statistical software, BASE-9, we derive precise cluster parameters, identify single and binary cluster members, and extract their masses. We identify 571 binaries down to Gaia G = 20.3 and a lower-limit on the binary frequency of f_b = 0.41 +/- 0.02. We extend the binary demographics by many magnitudes faint-ward of previous (radial-velocity) studies of this cluster and further away from the cluster center (1.78-degrees, roughly 10 core radii). We find the binary stars to be more centrally concentrated than the single stars in the cluster. Furthermore, we find strong evidence for mass segregation within the binary population itself, with progressively more massive binary samples becoming more and more centrally concentrated. For the single stars, we find weaker evidence for mass segregation; only the most massive single stars (> 2.5MSun) appear more centrally concentrated. Given the cluster age of ~200 Myr, and our derived half-mass relaxation time for the cluster of 230 +/- 84 Myr, we estimate ~47% of the binary stars and ~12% of single stars in the cluster have had time to become dynamically mass segregated. Importantly, when we investigate only stars with mass segregation timescales greater than the cluster age, we still find the binaries to be more centrally concentrated than the singles, suggesting the binaries may have formed with a primordially different spatial distribution than the single stars.