paper

New members of the TW Hydrae Association and two accreting M-dwarfs in Scorpius-Centaurus

arXiv:1507.08002 · doi:10.1093/mnras/stv1745

Abstract

We report the serendipitous discovery of several young mid-M stars found during a search for new members of the 30-40 Myr-old Octans Association. Only one of the stars may be considered a possible Octans(-Near) member. However, two stars have proper motions, kinematic distances, radial velocities, photometry and Li I 6708AA measurements consistent with membership in the 8-10 Myr-old TW Hydrae Association. Another may be an outlying member of TW Hydrae but has a velocity similar to that predicted by membership in Octans. We also identify two new lithium-rich members of the neighbouring Scorpius-Centaurus OB Association (Sco-Cen). Both exhibit large 12 and 22 micron excesses and strong, variable H-alpha emission which we attribute to accretion from circumstellar discs. Such stars are thought to be incredibly rare at the ~16 Myr median age of Sco-Cen and they join only one other confirmed M-type and three higher-mass accretors outside of Upper Scorpius. The serendipitous discovery of two accreting stars hosting large quantities of circumstellar material may be indicative of a sizeable age spread in Sco-Cen, or further evidence that disc dispersal and planet formation time-scales are longer around lower-mass stars. To aid future studies of Sco-Cen we also provide a newly-compiled catalogue of 305 early-type Hipparcos members with spectroscopic radial velocities sourced from the literature.

12 pages. Accepted for publication in MNRAS

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