2003AJ....125.1407N

We carried out deep imaging observations of the Lupus 3 dark cloud in near-infrared J, H, and K_sbands. An area of ∼8'x8' was observed, which corresponds to a projected area of ∼0.4x0.4 pc at the distance of the cloud, ∼150 pc. Lupus 3 showed itself as a near-infrared nebula that has a surface brightness higher than the adjacent sky at all the three wavelengths. In a JHK_scolor composite image (blue, green, and red are assigned to J, H, and K_s, respectively), three dark red cores are surrounded by a blue halo. The surface brightness was measured with 5 σ limiting magnitudes of J=21.6, H=21.3, and K_s=20.6 mag arcsec^–2. The appearance of the nebula depends on the wavelength. In the J band, dark cores are surrounded by a brighter halo, while in the K_s band, the dark cores of the J band are bright except for the central part of two of the cores. The appearance in the H band is intermediate between those of the J and K_sbands, having dark cores surrounded by local maxima of the surface brightness and decreased surface brightness farther out. The surface brightness is J=20.6, H=19.8, and K_s=19.4 mag arcsec^–2 at the maximum in each band. Photometry of the point sources was done with 10 σ limiting magnitudes of J=20.1, H=18.8, and K_s=17.7. We constructed an extinction map of the background stars, using the H-K color of 1974 sources and the standard reddening law of Rieke & Lebofsky. The maximum value for the extinction is A_V=47 mag. There are three local maxima of the extinction with A_V≳30 mag, which we consider to be dense cores. Their positions agree with the cores identified with the surface brightness appearance. The surface brightness and its relationship with the extinction are understood in terms of scattering of starlight by dust. The values of the maximum surface brightness can be explained by scattering of starlight by dust in the cloud if we adopt a model of grain size distribution by Weingartner & Draine.