A Census of the Chamaeleon I Star-Forming Region

Abstract

Optical spectroscopy has been obtained for 179 objects that have been previously identified as possible members of the cluster, that lack either accurate spectral types or clear evidence of membership, and that are optically visible (I<18). I have used these spectroscopic data and all other available constraints to evaluate the spectral classifications and membership status of a total sample of 288 candidate members of Chamaeleon I that have appeared in published studies of the cluster. The latest census of Chamaeleon I now contains 158 members, 8 of which are later than M6 and thus are likely to be brown dwarfs. I find that many of the objects identified as members of Chamaeleon I in recent surveys are actually field stars. Meanwhile, 7 of 9 candidates discovered by Carpenter and coworkers are confirmed as members, one of which is the coolest known member of Chamaeleon I at a spectral type of M8 (~0.03 M_sun). I have estimated extinctions, luminosities, and effective temperatures for the members and used these data to construct an H-R diagram for the cluster. Chamaeleon I has a median age of ~2 Myr according to evolutionary models, and hence is similar in age to IC 348 and is slightly older than Taurus (~1 Myr). The measurement of an IMF for Chamaeleon I from this census is not possible because of the disparate methods with which the known members were originally selected, and must await an unbiased, magnitude-limited survey of the cluster.

59 pages, 22 figures

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