Protostellar accretion disks resolved with the JCMT-CSO interferometer

Abstract

The James Clark Maxwell Telescope-Caltech Submillimeter Observatory (JCMT-CSO) submillimeter interferometer was used to measure the size and orientation of the compact dust continuum emission at 870 micrometers from the protostellar sources HL Tau and L1551 IRS 5. Assuming an elliptical Gaussian for the brightness distribution and distances of 140 pc, the data are well fitted by semi-major radii to half-maximum brightness and position angles of 60 AU at 126 deg for HL Tau and 80 AU at 162 deg for L1551. An upper limit of 50 AU (0.4 sec) 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 emission is perpendicular to the outflow axes, as expected for accretion disks. The high brightness indicates substantial column density and mass, further strengthening the accretion disk interpretation. Our observations do not strongly constrain the disk mass; applying an accretion disk model to our data gives a lower limit of approximately 0.02 solar mass for both sources.