The molecular disk surrounding the protostellar binary L1551 IRS5

The inner three arcminutes surrounding the Class 0/1 binary protostar L1551 IRS5 have been observed using the J = 1 → 0 transitions of the HCO, HCO, CO and CO molecular species. Since the line core of HCO is self reversed over a substantial part of our map, observations of isotopomers such as HCO are required in order to estimate the mass of the molecular gas in the immediate vicinity of IRS5. Our observations demonstrate the presence of a large (∼7000 AU radius) dense, possibly rotating, molecular disk with a mass of a few M oriented perpendicular to the major axis of an extended molecular outflow. The disk is surrounded by an envelope with a radius of ∼10 000 AU that contains two massive (each ∼1 M ) clumps. One of these features appears to be kinematically disconnected from both the disk and the molecular outflow.