Orbital Parameters and Binary Properties of 37 FGK stars in the Cores of Open Clusters NGC 2516 and NGC 2422

TL;DR

This study derives orbital parameters for 37 binaries in two open clusters using radial velocity data and Gaia measurements, revealing insights into binary properties and evolution in cluster environments.

Contribution

First detailed orbital analysis of binaries in NGC 2516 and NGC 2422 using Gaia data and MCMC fitting, enhancing understanding of binary evolution in young clusters.

Findings

Identification of two short-period binaries with potential tidal circularization.

Discovery of a binary with a brown dwarf secondary.

Detection of additional companions in some cluster members.

Abstract

We present orbits for 24 binaries in the field of open cluster NGC 2516 (~150 Myr) and 13 binaries in the field of open cluster NGC 2422 (~130 Myr) using results from a multi-year radial velocity survey of the cluster cores. Six of these systems are double-lined spectroscopic binaries (SB2s). We fit these RV variable systems with orvara, a MCMC-based fitting program that models Keplerian orbits. We use precise stellar parallaxes and proper motions from Gaia EDR3 to determine cluster membership. We impose a barycentric radial velocity prior on all cluster members; this significantly improves our orbital constraints. Two of our systems have periods between 5 and 15 days, the critical window in which tides efficiently damp orbital eccentricity. These binaries should be included in future analyses of circularization across similarly-aged clusters. We also find a relatively flat distribution of binary mass ratios, consistent with previous work. With the inclusion of TESS lightcurves for all available targets, we identity target 378-036252 as a new eclipsing binary. We also identify a field star whose secondary has a mass in the brown dwarf range, as well as two cluster members whose RVs suggest the presence of an additional companion. Our orbital fits will help constrain the binary fraction and binary properties across stellar age and across stellar environment.