PROTOSTELLAR ACCRETION DISKS RESOLVED WITH THE JCMT-CSO INTERFEROMETER

The JCMT-CSO submillimeter interferometer was used to measure the size and orientation of the compact dust continuum emission at 870 mum fro m the protostellar sources HL Tau and L1551 IRS 5. Assuming an ellipti cal Gaussian for the brightness distribution and distances of 140 pc, the data are well fitted by semi-major radii to half-maximum brightnes s and position angles of 60 AU at 126-degrees for HL Tau and 80 AU at 162-degrees for L1551. An upper limit of 50 AU (0''.4) is set for the radii along the minor axes, leading to minimum brightness temperatures of 36 K and 28 K, respectively. The elongation in the continuum emiss ion is perpendicular to the outflow axes, as expected for accretion di sks. The high brightness indicates substantial column density and mass , further strengthening the accretion disk interpretation. Our observa tions do not strongly constrain the disk mass; applying an accretion d isk model to our data gives a lower limit of approximately 0.02 M. for both sources.