The structure of the NGC 1333 - IRAS 2 protostellar system on 500 AU scales

This paper investigates small-scale (500 AU) structures of dense gas and dust around the low-mass protostellar binary NGC 1333-IRAS2 using millimeter-wavelength aperture-synthesis observations from the Owens Valley and BerkeleyIllinois-Maryland-Association interferometers. The detected λ = 3 mm continuum emission from cold dust is consistent with models of the envelope around IRAS2A, based on previously reported submillimeter-continuum images, down to the 3′′, or 500 AU, resolution of the interferometer data. Our data constrain the contribution of an unresolved point source to 22 mJy. 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 >∼0.3 M . The same envelope model also reproduces aperturesynthesis 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 IRAS2C. We hypothesize that N2H is destroyed through reactions with CO that is released from icy grains near the protostellar sources IRAS2A 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 IRAS2A, a north-south velocity gradient near this source indicates a second, perpendicular outflow. This suggests the presence of a binary companion within 0. ′′3 (65 AU) from IRAS2A 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.