Small-Scale Structure of Candidates for Protostellar Collapse. I. BIMA Observations of L1527 and CB 54

Aperture synthesis observations of L1527 and CB 54 were made in the 13CO and C18O J = 1 → 0 lines using the BIMA interferometers, in order to probe the small-scale structure of the gas distribution and to test the collapse picture in these two sources. In L1527, a bipolar outflow is detected in 13CO with an opening angle of 50° and its axis in the plane of the sky along the east-west direction. The profile difference between the 13CO and C18O J = 1 → 0 lines toward the center position is consistent with the signature of infall, as suggested by previous single-dish observations of L1527. In CB 54, a bipolar outflow is seen in 13CO; one of the redshifted outflow peaks is less than 10" from the center position, making it difficult to pick out possible signatures of infall. We have made radiative transfer models for L1527 based on the collapse solution of a rotating cloud by Terebey, Shu, & Cassen. The best-fit parameters are as follows: the effective sound speed, a = 0.25 km s-1; the infall radius, rinf = 0.026 pc; the H2CO abundance, X(H2CO) = 4 × 10-9 and the C18O abundance, X(C18O) = 1.4 × 10-7. The model can reproduce the observed profiles of single-dish observations and also the qualitative feature of the interferometric observations. Comparisons are made with other models for L1527 in the literature.