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[78.08] The eta Chamaeleontis cluster and TW Hydrae association: a common origin in the Sco-Cen OB association

E.E. Mamajek (Steward Obs.), E.D. Feigelson (PSU), W.A. Lawson (UNSW/ADFA)

The eta Chamaeleontis open cluster is a newly-discovered (Mamajek, Lawson & Feigelson 1999, ApJL, 516, 77) young (~ 8 Myr) compact (< 1 pc extent) cluster of 13 known systems at a distance of 97 pc. It is the fourth-closest compact cluster, and the second-closest grouping of T Tauri stars following the TW Hydrae association. Remarkably, proper motion analysis suggests a common origin for eta Cha and TW Hya, and other isolated young stars across the greater Cha region, in the Sco-Cen OB association ~10 Myr ago. We conclude the Sco-Cen association is vastly greater in extent than previously recognised; eta Cha and TW Hya are situated ~30 deg. either side of the Lower Centarus-Crux subgroup. eta Cha and TW Hya are unlikely to be unique structures.