Abstract

Contributed Talk - Splinter CloseBinaries   (MW-0250)

A Close Look at the Multiplicity of Young Massive Stars in Galactic Embedded Clusters

C. Nagar., L. Labadie, F. Peissker, E. Bordier
Universität zu Köln

The formation of stellar multiples is a frequent outcome of massive star formation and early cluster evolution. Characterising stellar multiplicity rates, separations, and mass ratios provides essential constraints for star formation theories and for understanding how natal cluster envi- ronments shape the process. However, the multiplicity of young massive stars remains poorly constrained, as they form in small numbers within distant, heavily obscured environments, mak- ing direct observation during their first few million years particularly challenging. In this work, we investigate close multiplicity (separations < 3000 AU) of young massive stars in four embed- ded clusters at distances of 1.3–1.75 kpc and ages of 1–2.75 Myr. Using VLT/NACO adaptive-optics K-band images across multiple fields of DBS 113, DBS 121, Hourglass, and RCW 108 — four Galactic massive star clusters at Z ∼ Z⊙ — we detect sources down to K ≈ 18 around cluster members identified through (J − H), (H − K) colour–colour analysis of VVV/VIRAC data. The likelihood of companionship is evaluated through chance- alignment probabilities using stellar density estimates from the Besançon population synthe- sis model. Multiple systems are classified into hierarchical configurations using dendrogram- clustering to derive multiplicity statistics. We obtain multiplicity fractions (MF) and compan- ion fractions (CF) across separation bins up to 3000 au. Over 1 to 3 Myr, we find a decay in multiplicity with MF declining from 0.54 to 0.31 and CF from 0.73 to 0.56. This suggests rapid dynamical processing of native stellar multiples. The reported multiplicity properties are put in perspective with the overall stellar content of the clusters, characterised in terms of mass func- tion, spectral type, and infrared excess of the young stars detected at near-infrared wavelengths. Together, these results provide observational constraints on the early multiplicity of massive stars and offer a basis for quantifying how cluster environments could shape the evolution of multiple stellar systems