Common Proper Motion Companions to Nearby Stars: Ages and Evolution

TL;DR

This study investigates 41 nearby stars with wide binary and CPM companions, estimating their ages, discovering new companions, and analyzing their dynamical evolution, revealing that most are young thin disk stars with complex hierarchical systems.

Contribution

It provides new identifications of CPM companions, estimates their ages using activity indicators, and explores their dynamical properties and evolutionary states.

Findings

Discovered 10 new CPM companions, including three at extreme separations.

Most CPM companions are young, thin disk stars under 1 Gyr old.

Over 25% of CPM systems are hierarchical multiples or binaries.

Abstract

A set of 41 nearby stars (closer than 25 pc) is investigated which have very wide binary and common proper motion (CPM) companions at projected separations between 1000 and $200 000$ AU. These companions are identified by astrometric positions and proper motions from the NOMAD catalog. Based mainly on measures of chromospheric and X-ray activity, age estimation is obtained for most of 85 identified companions. Color -- absolute magnitude diagrams are constructed to test if CPM companions are physically related to the primary nearby stars and have the same age. Our carefully selected sample includes three remote white dwarf companions to main sequence stars and two systems (55 Cnc and GJ 777A) of multiple planets and distant stellar companions. Ten new CPM companions, including three of extreme separations, are found. Multiple hierarchical systems are abundant; more than 25% of CPM components are spectroscopic or astrometric binaries or multiples themselves. Two new astrometric binaries are discovered among nearby CPM companions, GJ 264 and HIP 59000 and preliminary orbital solutions are presented. The Hyades kinematic group (or stream) is presented broadly in the sample, but we find few possible thick disk objects and none halo stars. It follows from our investigation that moderately young (age $\lesssim 1$ Gyr) thin disk dwarfs are the dominating species in the near CPM systems, in general agreement with the premises of the dynamical survival paradigm. Some of the multiple stellar systems with remote CPM companions probably undergo the dynamical evolution on non-coplanar orbits, known as the Kozai cycle.