Simon J. Murphy, Warrick A. Lawson, Michael S. Bessell
We present a comprehensive investigation of the {\epsilon} Chamaeleontis association ({\epsilon} Cha), one of several stellar groups in the southern sky kinematically linked to the Scorpius-Centaurus OB association (Sco-Cen). We reassess the putative membership of {\epsilon} Cha using the best-available proper motions (Hipparcos, Tycho-2 and SPM4) with radial velocity and lithium data from the literature and new ANU 2.3-m/WiFeS spectroscopy. After applying a convergence analysis our final membership comprises 35-41 stars from B9 to mid-M spectral types, with a mean distance of 110+/-7 pc and a mean space motion of (U,V,W)=(-10.9,-20.4,-9.9) km/s. Theoretical evolutionary models suggest {\epsilon} Cha is 3-5 Myr old, distinguishing it as the youngest association in the solar neighbourhood. Considering all the available evidence we reject several stars proposed as members in the literature and suggest they may belong to the background Cha I and II clouds or other nearby young groups. Our analysis underscores the importance of a holistic and conservative approach to assigning young stars to kinematic groups, many of which have only subtly different properties and ill-defined memberships. Fifteen {\epsilon} Cha members show 3-22 {\mu}m spectral energy distributions attributable to circumstellar discs, including 11 stars which appear to be accreting. Multi-epoch spectroscopy reveals three M-type members with broad and highly-variable H{\alpha} emission as well as several new spectroscopic binaries. We conclude with a discussion of {\epsilon} Cha's connection to the young open cluster {\eta} Cha and the Lower Centaurus Crux (LCC) subgroup of Sco-Cen. Contrary to earlier studies which assumed {\eta} and {\epsilon} Cha are coeval and were born in the same location, we find the groups were separated by ~30 pc when {\eta} Cha formed first in the outskirts of LCC.
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http://arxiv.org/abs/1305.4177
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