A Near-Infrared Imaging Survey of the Lupus 3 Dark Cloud: A Modest Cluster of Low-Mass, Pre–Main-Sequence Stars

Abstract

We present the first report on results of a near-infrared imaging survey of the Lupus 3 dark cloud. This cloud is known to be associated with a modest cluster of T Tauri stars from a previous optical Hα emission-line star survey. The survey covers 7′ × 11′, which corresponds to a projected area of ∼0.35 × 0.55 pc at a distance of 150 pc. Mapping was carried out at J, H, and Ks, to 10 σ limiting magnitudes of J = 17.0, H = 16.5, and Ks = 15.5. A total of 229 sources brighter than Ks < 15.8 were detected at all bands with a 90% completeness limit. Source classification is performed based on the near-infrared colors. Ten sources are candidates of Lada's Class II pre-main-sequence (PMS) stars, as they have a color excess that cannot be explained by reddening resulting from interstellar dust. We also identified 11 Class I-like candidates that were not detected at J and have a large color excess (H- Ks ≥ 2), which is unlikely to arise from extinction in the Lupus dark cloud. There are four subclusters in this survey area of which three are embedded and mainly consist of the Class I-like candidates. The average density of PMS stars is around 500 pc-3, suggesting the presence of a modest cluster of embedded PMS stars. We estimate masses of the Class II candidates with aid of an evolutionary model of PMS stars. Ten of them have masses less than 0.08 M⊙ if we assume their age to be 106 yr. Hence, we consider them to be young brown dwarf (YBD) candidates. The relative population of YBDs in the Lupus 3 dark cloud is larger than in the Taurus.