2004A&A...413..993J

This paper investigates small-scale (500AU) structures of dense gas and dust around the low-mass protostellar binary NGC 1333-IRAS 2 using millimeter-wavelength aperture-synthesis observations from the Owens Valley and Berkeley-Illinois-Maryland-Association interferometers. The detected λ=3 mm continuum emission from cold dust is consistent with models of the envelope around IRAS 2A, based on previously reported submillimeter-continuum images, down to the 3", or 500AU, resolution of the interferometer data. Our data constrain the contribution of an unresolved point source to 22mJy. The importance of different parameters, such as the size of an inner cavity and impact of the interstellar radiation field, is tested. Within the accuracy of the parameters describing the envelope model, the point source flux has an uncertainty by up to 25%. We interpret this point source as a cold disk of mass >0.3M_☉. The same envelope model also reproduces aperture-synthesis line observations of the optically thin isotopic species C³⁴S and H¹³CO⁺. The more optically thick main isotope lines show a variety of components in the protostellar environment: N₂H⁺ is closely correlated with dust concentrations as seen at submillimeter wavelengths and is particularly strong toward the starless core IRAS 2C. We hypothesize that N₂H⁺ is destroyed through reactions with CO that is released from icy grains near the protostellar sources IRAS 2A and B. CS, HCO⁺, and HCN have complex line shapes apparently affected by both outflow and infall. In addition to the east-west jet seen in SiO and CO originating from IRAS 2A, a north-south velocity gradient near this source indicates a second, perpendicular outflow. This suggests the presence of a binary companion within 0."3 (65AU) from IRAS 2A as driving source of this outflow. Alternative explanations of the velocity gradient, such as rotation in a circumstellar envelope or a single, wide-angle (90°) outflow are less likely.