{
  "id": "1305.4177",
  "version": "v2",
  "published": "2013-05-17T20:00:01.000Z",
  "updated": "2013-07-23T19:51:36.000Z",
  "title": "Re-examining the membership and origin of the Epsilon Cha association",
  "authors": [
    "Simon J. Murphy",
    "Warrick A. Lawson",
    "Michael S. Bessell"
  ],
  "comment": "24 pages. Accepted for publication in MNRAS (23/7/2013). Accepted version with updated text and new discussion of the Epsilon Cha disc fraction. Table B1 available on request",
  "categories": [
    "astro-ph.SR"
  ],
  "abstract": "We present a comprehensive investigation of the Epsilon Chamaeleontis association (Epsilon Cha), one of several young moving groups spread across the southern sky. We re-assess the putative membership of Epsilon Cha using the best-available proper motion and spectroscopic measurements, including new ANU 2.3-m/WiFeS observations. 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 and a mean space motion of (U,V,W)=(-10.9+/-0.8,-20.4+/-1.3,-9.9+/-1.4) km/s. Theoretical evolutionary models suggest Epsilon Cha is 3-5 Myr old, distinguishing it as the youngest moving group in the solar neighbourhood. Fifteen members show 3-22 micron spectral energy distributions attributable to circumstellar discs, including 11 stars which appear to be actively accreting. Epsilon Cha's disc and accretion fractions (29+8-6 and 32+9-7 per cent, respectively) are both consistent with a typical 3-5 Myr-old population. Multi-epoch spectroscopy reveals three M-type members with broad and highly-variable H-alpha emission as well as several new spectroscopic binaries. 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. 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. We conclude with a brief discussion of Epsilon Cha's connection to the young open cluster Eta Cha and the Sco-Cen OB association. 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 Sco-Cen, 1-3 Myr before the majority of Epsilon Cha members.",
  "revisions": [
    {
      "version": "v2",
      "updated": "2013-07-23T19:51:36.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "epsilon cha association",
      "membership",
      "spectral energy distributions attributable",
      "young open cluster eta cha"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1093/mnras/stt1375",
      "journal": "Monthly Notices of the Royal Astronomical Society",
      "year": 2013,
      "month": "Oct",
      "volume": 435,
      "number": 2,
      "pages": 1325
    },
    "note": {
      "typesetting": "TeX",
      "pages": 24,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1234162,
      "adsabs": "2013MNRAS.435.1325M"
    }
  }
}