Quantify the role of hierarchical triples in NGC 6791

Quantify the role of hierarchical triples in the dynamical evolution and present-day multiplicity of the open cluster NGC 6791.

Background

The paper studies the unusually high binary fraction and excess of high-mass-ratio binaries in the old, dynamically evolved open cluster NGC 6791. It also identifies stars lying above the equal-mass binary sequence as candidate unresolved triple or higher-order systems.

Although hierarchical triples are theoretically expected to form efficiently in dense cluster cores through binary–binary interactions, their contribution to the observed multiplicity and dynamical processing of NGC 6791 has not been quantitatively established. The paper presents photometric evidence for candidate triples but does not determine their formation history, survival rate, or dynamical influence.

References

the role of hierarchical triples—which are theoretically predicted to form efficiently in high-density cores via binary–binary interactions (N. W. C. Leigh & A. M. Geller 2013)—remains poorly quantified in this cluster.

— Evidence for Dynamical Filtering: High Binary Fraction, Hard-binary Excess, and Unresolved Triples in the Surviving Core of NGC 6791  (2608.13955 - Chi et al., 14 Aug 2026) in Section 1, Introduction, page 2