Substellar Objects in Nearby Young Clusters (SONYC). III. Chamaeleon-I

SONYC—Substellar Objects in Nearby Young Clusters—is asurvey program to investigate the frequency and properties of substellarobjects with masses down to a few times that of Jupiter in nearbystar-forming regions. In this third paper, we present our recent resultsin the Chamaeleon-I star-forming region. We have carried out deepoptical and near-infrared imaging in four bands (I, z, J, KS) using VIMOS on the European Southern Observatory Very Large Telescope(VLT) and SOFI on the New Technology Telescope, and combined our datawith mid-infrared data from the Spitzer Space Telescope. The surveycovers ~0.25 deg2 on the sky and reaches completeness limitsof 23.0 in the I band, 18.3 in the J band, and 16.7 in the KSband. Follow-up spectroscopy of the candidates selected from the opticalphotometry (I ≲ 21) was carried out using the multi-object spectrograph VIMOS on the VLT. We identify 13 objects consistent with M spectral types, 11 of which are previously known M dwarfs with confirmed membership in the cluster. The two newly reported objects have effective temperatures above the substellar limit. We also present two new candidate members of Chamaeleon-I, selected from our JK photometry combined with the Spitzer data. Based on the results of our survey, we estimate that the number of missing very low mass members down to ∼0.008 M⊙ and AV ≤ 5 is ≤7, i.e., ≤3% of the total cluster population according to the current census.