Protostars and Planets VI, Heidelberg, July 15-20, 2013
A fresh look at the 3-5 Myr-old Epsilon Cha association
Murphy, Simon (ARI/ZAH Heidelberg)
Lawson, Warrick (University of New South Wales, Canberra)
Bessell, Michael (Australian National University)
We present a comprehensive investigation of the Epsilon Chamaeleontis association, one of several young moving groups in the southern sky. Despite being an ideal laboratory to study circumstellar disc evolution around low-mass stars, Epsilon Cha remains one of the least-understood young moving groups in the solar neighbourhood. Our work aims to improve the membership, kinematics and age of Epsilon Cha, investigate its disc and accretion properties and its relationship to the nearby benchmark open cluster Eta Cha. After applying a kinematic analysis our final membership comprises 35-41 stars from B9 to mid-M spectral types, with a mean distance of 110 +/- 7 pc. Theoretical evolutionary models suggest the association is 3-5 Myr old, distinguishing it as the youngest nearby moving group. Fifteen members show 3-22 um spectral energy distributions attributable to circumstellar discs, including 11 stars which appear to be actively accreting. Both the disc and accretion fractions are consistent with a typical 3-5 Myr-old population. We reject 11 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. 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 4-8 Myr ago in the outskirts of the Sco-Cen OB association, 1-3 Myr before the Epsilon Cha.
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