THE CIRCUMSTELLAR MOLECULAR CORE AROUND L1551-IRS-5

We present maps of (CO)-O-18 and (CO)-O-17 J = 2 --> 1 emission toward the embedded young star L1551 IRS 5. The (CO)-O-17 emission traces a compact region similar to 1900 AU in radius which is centered on the s tar which contains similar to 0.1 M. of material. The integrated (CO)- O-17 emission has a crosslike structure aligned in the cardinal direct ions which is very similar to the structure seen in the submillimeter continuum emission from this source. A spatially more extended compone nt of material which contains an additional 0.1 M. of material within 20 '' of IRS 5, also contributes to the (CO)-O-17 emission. The cross gas is warmer and has a larger velocity dispersion than the more exten ded gas. The motions of the extended material imply a virial mass of 1 -3 M., which is dominated by the mass of the central star plus disk. T he (CO)-O-18 lines have considerable line wing emission and part of th e cross is evident in this wing emission. Comparison with existing map s of the outflow near IRS 5 suggests that the cross material is part o f the heated wall of the cavity evacuated by the outflow. The presence of such structures near embedded stars complicates the search for acc reting material. However, the properties of the extended (CO)-O-17 emi ssion constrain the mass accretion rate in L1551 IRS 5 to be less than 1.4 x 10(-5) M. yr(-1). Comparison with the observed mass outflow rat e from IRS 5 at a similar size scale suggests that there is currently little or no net accretion of material from the larger scale dense cor e into the central 2000 AU radius region about IRS 5.