Berkeley-Illinois-Maryland association survey of protostellar collapse candidates in HCO+ and HCN lines

We observed protostellar collapse candidates in the lambda = 3.4 mm continuum, the HCO+ J = 1 --> 0 line, and the HCN J=1-->0 line using the Berkeley-Illinois-Maryland Association interferometer. Regions observed are NGC 1333 IRAS 4, L1527, HH 25 MMS, IRAS 16293-2422, Serpens SMM 4/2, B335, IRAS 20050+2720, and L1157. These sources were selected from their infall signature (blue-skewed line profile) in a single-dish survey of class 0 sources (Gregersen et al.). In our HCO+ and HCN spectra, most of the sources show the blueshifted side stronger than the redshifted side, which is consistent with the selection criteria. IRAS 16293 and IRAS 20050B line profiles are more complicated than a simple blue-skewed profile. Serpens SMM 2 shows symmetric, single-peaked line profiles. Most of the sources in our survey drive molecular outflows. We found that NGC 1333 IRAS 4A/B, L1527, B335, and L1157 are strong cases for protostellar collapse with relatively simple structures suitable for detailed study. The HCN spectrum toward IRAS 16293 shows that its infall signature from other molecular lines needs careful interpretation. HH 25 MMS, Serpens SMM 2-4, and IRAS 20050A/B are embedded in clouds with complex structure and prone to confusion.