A near-infrared imaging survey of the Lupus 3 dark cloud: A modest clusterof low-mass, pre-main-sequence stars

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 H alpha emission-line sta r survey. The survey covers 7' x 11', which corresponds to a projected area of similar to 0.35 x 0.55 pc at a distance of 150 pc. Mapping was carried out at J, H, and K-s, to 10 sigma limiting magnitudes of J = 17.0, H = 16.5 , and K-s = 15.5. A total of 229 sources brighter than K-s < 15.8 were dete cted at all bands with a 90% completeness limit. Source classification is p erformed based on the near-infrared colors. Ten sources are candidates of L ada's Class II pre-main-sequence (PMS) stars, as they have a color excess t hat cannot be explained by reddening resulting from interstellar dust. We a lso identified 11 Class I-like candidates that were not detected at J and h ave a large color excess (H-K-s greater than or equal to 2), which is unlik ely to arise from extinction in the Lupus dark cloud. There are four subclu sters 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 50 0 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 10(6) 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.