THE MOLECULAR-STRUCTURE AROUND HL TAURI

High-resolution (2."7) observations of (CO)-C-13 (1-0) emission around the young star HL Tauri confirm the presence of circumstellar gas distributed in an elongated structure. Thermal continuum emission, centered on the stellar position, is unresolved (radius less-than-or-equal-to 190 AU) and suggests a mass greater-than-or-equal-to 0.l M. The (CO)-C-13 extends along PA 160-degrees to radii of almost 2000 AU but is less than 380 AU in width. Extended molecular emission is observed only at velocities close to the systemic value, about 6.6 km s-1. Higher velocity gas, and most of the system mass, is confined to a core of radius less-than-or-equal-to 190 AU. Satellite condensations, with masses only a few percent of the main concentration, are also observed; these must be less than 100 AU in size to survive. The general form of the rotation curve is consistent with the gas moving in bound orbits about the central star. A low-velocity molecular feature, emanating from the stellar position along the disk axis, may be a low-velocity neutral flow from the disk itself