Abstract
We present the results of a survey of the Coma Berenices open star cluster (Melotte 111), undertaken using proper motions from the USNO-B1.0 (United States Naval Observatory) and photometry from the Two-Micron All-Sky Survey (2MASS) Point Source catalogues. We have identified 60 new candidate members with masses in the range 1.007 < M < 0.269 M⊙. For each we have estimated a membership probability by extracting control clusters from the proper motion vector diagram. All 60 are found to have greater than 60 per cent probability of being members, more than doubling the number of known cluster members. The new luminosity function for the cluster peaks at bright magnitudes, but is rising at K≈ 12, indicating that it is likely that lower mass members may exist. The mass function also supports this hypothesis.
Highlights
During the last two decades there have been numerous deep surveys of young nearby open clusters focusing on the detection of very low-mass stellar and substellar members (e.g. Jameson & Skillen 1989; Lodieu et al 2005)
In this paper we report on our efforts to use the USNO-B1.0 and 2MASS Point Source catalogues to search for further candidate low-mass members of Melotte 111
We believe that our survey is reasonably complete to this limit; we tried proper motion search radii of 7 and 5 mas yr−1, but in both cases found that increasing numbers of likely members were excluded
Summary
During the last two decades there have been numerous deep surveys of young nearby open clusters focusing on the detection of very low-mass stellar and substellar members (e.g. Jameson & Skillen 1989; Lodieu et al 2005). Reid 1993; Gizis, Reid & Monet 1999; Moraux, private communication) This finding is loosely in agreement with the predictions of N-body simulations which indicate that less than one-fifth of the original population of substellar members remains tidally bound to a cluster at the age of the Hyades, 625 ± 50 Myr (Perryman et al 1998). Argue & Kenworthy (1969) performed a photographic UBVI survey of a circular field, 3◦.3 in diameter, to a limiting depth of m P = 15.5 They rejected all but two of Artyukhina’s candidates with m P > 11 but identified a further two faint objects with photometry and proper motion which they deemed to be consistent with cluster membership. State-of-the-art evolutionary models indicate that some of these objects have masses of only M ≈ 0.269 M
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