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 star which contains similar to 0.1 M. of material. The integrated (CO)-O-17 emission has a crosslike structure aligned in the cardinal directions which is very similar to the structure seen in the submillimeter continuum emission from this source. A spatially more extended component 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 extended 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. The (CO)-O-18 lines have considerable line wing emission and part of the cross is evident in this wing emission. Comparison with existing maps of the outflow near IRS 5 suggests that the cross material is part of the heated wall of the cavity evacuated by the outflow. The presence of such structures near embedded stars complicates the search for accreting material. However, the properties of the extended (CO)-O-17 emission 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 rate 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 core into the central 2000 AU radius region about IRS 5.