Dynamical detection of three triple stellar systems in open clusters

TL;DR

This study identifies and analyzes three hierarchical triple star systems in open clusters using radial velocity data, revealing their orbital configurations and discussing their dynamical evolution, including Kozai cycles.

Contribution

The paper presents the first detailed kinematic analysis of three triple stellar systems in open clusters, deriving their orbital parameters and discussing their dynamical evolution.

Findings

Two systems in NGC2516 have similar orbital configurations.

The young system HD315031 has a highly eccentric outer orbit.

Including previous data, NGC2516 hosts five hierarchical triples.

Abstract

We present a kinematic analysis of three triple stellar systems belonging to two open clusters: CPD-60{\deg}961 and HD66137 in NGC2516, and HD315031 in NGC6530. All three systems are hierarchical triples with a close binary bound to a third body in a wider orbit, whose presence is detected through velocity variations of the close binary barycentre. Orbital parameters are derived from radial velocity curves. Absolute parameters for all stars are estimated assuming cluster membership. Some dynamical and evolutionary aspects of these systems are discussed, particularly the possible influence of Kozai cycles. The two systems of NGC2516 have similar orbital configurations with inner periods of 11.23 d and 8.70 d and outer periods of 9.79 yr and 9.24 yr. We report also radial velocity measurements of the components of the visual binary CPD-60{\deg}944 in NGC2516. Including results from previous works, this cluster would harbor 5 hierarchical triples. The young system HD315031 has an inner binary with a period of 1.37 d and a very eccentric (e=0.85) outer orbit with a period of 483 d. Possible dynamical evolutionary scenarios are discussed. Long-term radial velocity monitoring is highlighted as strategy for the detection of subsystems with intermediate separations, which are hard to cover with normal spectroscopic studies or visual techniques.