The Stellar Population of the Chamaeleon I Star-forming Region

I present a new census of the stellar population in the Chamaeleon I star-forming region. Using optical and near-IR photometry and follow-up spectroscopy, I have discovered 50 new members of Chamaeleon I, expanding the census of known members to 226 objects. Fourteen of these new members have spectral types later than M6, which doubles the number of known members that are likely to be substellar. I have estimated extinctions, luminosities, and effective temperatures for the known members, used these data to construct an H-R diagram for the cluster, and inferred individual masses and ages with the theoretical evolutionary models of Baraffe and Chabrier. The distribution of isochronal ages indicates that star formation began 3-4 and 5-6 Myr ago in the southern and northern subclusters, respectively, and has continued to the present time at a declining rate. The IMF in Chamaeleon I reaches a maximum at a mass of 0.1-0.15 M_solar and thus closely resembles the IMFs in IC 348 and the Orion Nebula Cluster. In logarithmic units where the Salpeter slope is 1.35, the IMF is roughly flat in the substellar regime and shows no indication of reaching a minimum down to a completeness limit of 0.01 M_solar. The low-mass stars are more widely distributed than members at other masses in the northern subcluster, but this is not the case in the southern subcluster. Meanwhile, the brown dwarfs have the same spatial distribution as the stars out to a radius of 3° (8.5 pc) from the center of Chamaeleon I.

Based on observations performed with the Magellan Telescopes at Las Campanas Observatory, Cerro Tololo Inter-American Observatory (CTIO), Gemini Observatory, and the NASA/ESA Hubble Space Telescope (HST). CTIO is operated by the Association of Universities for Research in Astronomy (AURA) under a contract with the National Science Foundation (NSF). Gemini Observatory is operated by AURA under a cooperative agreement with the NSF on behalf of the Gemini partnership: the NSF (US), the Particle Physics and Astronomy Research Council (UK), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), CNPq (Brazil), and CONICET (Argentina). The HST observations are associated with proposal ID 10138 and were obtained at the Space Telescope Science Institute, which is operated by AURA under NASA contract NAS 5-26555.