Molecular outflows and star formation in the HL Tau stellar group

¹²CO(2-1) and ¹³CO(2-1) observations of the HL Tau/HH 30 region are presented. These observations have high sensitivity and spatial resolution, and allow a large scale study of the kinematics of the gas in this complex stellar group. The main result is that HL Tau drives a powerful extended molecular outflow that has probably blown out of its parental core on its blueward side. The red part of the flow is currently pushing its way into the denser remaining core gas. The total mass of outflowing gas is of the order of 0.17 M⊙ with 2/3 of this mass in the red part of the flow. The outflow rate is very high: 10^-5 M⊙, a value consistent with FU Orionis accretion rates. We also propose that the complex molecular outflow field that we have discovered is the result of several other molecular outflows that are possibly associated with the optical jets in this stellar group. We deduce from our data that the current constitution of this group consists of 3.6 M⊙ in gas and 2.0 M⊙ in stars, implying a high star formation efficiency which approaches 36%. We compute the gravitational energy of the core and find that the HL Tau system probably remains bound in spite of its current outflow activity.