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A deep photometric survey of the η Chamaeleontis cluster down to the brown dwarf – planet boundary
Authors:A-Ran Lyo  Inseok Song  Warrick A Lawson  M S Bessell  B Zuckerman
Institution:Academia Sinica Institute of Astronomy and Astrophysics, PO Box 23-141, Taipei 106, Taiwan;Gemini Observatory, 670 North A'ohoku Place, Hilo, HI 96720, USA;School of Physical, Environmental and Mathematical Sciences, University of New South Wales, Australian Defence Force Academy, Canberra, ACT 2600, Australia;Research School of Astronomy and Astrophysics, Institute of Advanced Studies, The Australian National University, Cotter Road, Weston Creek ACT 2611, Australia;Department of Physics and Astronomy and Center for Astrobiology, University of California, Los Angeles, CA 90095-1562, USA
Abstract:We report the outcome of the deep optical/infrared photometric survey of the central region (33 × 33 arcmin2 or 0.9 pc2) of the η Chamaeleontis (η Cha) pre-main sequence star cluster. The completeness limits of the photometry are I = 19.1, J = 18.2 and H = 17.6, faint enough to reveal low-mass members down to the brown dwarf and planet boundary of ≈13 MJup. We found no such low-mass members in this region. Our result combined with a previous shallower ( I = 17) but larger area survey indicates that low-mass objects  (0.013 < M /M < 0.075)  were either not created in the η Cha cluster or lost due to the early dynamical history of the cluster and ejected to outside the surveyed areas.
Keywords:stars: fundamental parameters  stars: pre-main-sequence  open clusters and associations: individual: η Chamaeleontis
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