Journal Article

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

Simon J. Murphy, Warrick A. Lawson and Michael S. Bessell

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 424, issue 1, pages 625-634
Published in print July 2012 | ISSN: 0035-8711
Published online July 2012 | e-ISSN: 1365-2966 | DOI:
RX J0942.7−7726AB: an isolated pre-main-sequence wide binary

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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 η 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 η Cha and a trace-back analysis argues for its birth in or near the Scorpius–Centaurus OB association (Sco–Cen). 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 ± 1.0 km s−1) 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.

Keywords: binaries: visual; stars: formation; stars: kinematics and dynamics; stars: low-mass; stars: pre-main-sequence; open clusters and associations

Journal Article.  8698 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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