RX J0942.7-7726AB: an isolated pre-main sequence wide binary

TL;DR

This paper reports the discovery of a wide binary system of two young M-dwarfs, likely formed near the Scorpius-Centaurus OB Association, providing insights into the formation and survival of fragile stellar systems.

Contribution

It presents the identification and characterization of a new wide binary system of young stars, linking it to the Sco-Cen association and discussing its possible origin and dynamical stability.

Findings

The binary system is approximately 8-12 Myr old.

The stars are separated by 4000-6000 AU.

The system's radial velocity suggests it may be unbound.

Abstract

We report the discovery of two young M-dwarfs, RX J0942.7-7726 (M1) and 2MASS J09424157-7727130 (M4.5), that were found only 42 arcsec apart in a survey for pre-main sequence stars surrounding the open cluster eta Chamaeleontis. Both stars have congruent proper motions and near-infrared photometry. Medium-resolution spectroscopy reveals that they are coeval (age 8-12 Myr), codistant (100-150 pc) and thus almost certainly form a true wide binary with a projected separation of 4000-6000 AU. The system appears too old and dynamically fragile to have originated in eta Cha and a traceback analysis argues for its birth in or near the Scorpius-Centaurus OB Association. RX J0942.7-7726AB joins a growing group of wide binaries kinematically linked to Sco-Cen, suggesting that such fragile systems can survive the turbulent environment of their natal molecular clouds while still being dispersed with large velocities. Conversely, the small radial velocity difference between the stars (2.7 \pm 1.0 km/s) could mean the system is unbound, a result of the coincidental ejection of two single stars with similar velocity vectors from the OB association early in its evolution.