A MOLECULAR DISK AND DENSE OUTFLOW IN CORONA-AUSTRALIS

The central region of the molecular outflow in the R Coronae Australis cloud was mapped in HCO+(J = 1 - 0), (HCO+)-C-13(J = 1 - 0), HCO+(J = 3 - 2) and (CO)-O-18(J = 2 - 1) with the SEST. In addition to the map s, selected positions were observed in SiO(J = 2 - 1, v = O). The obse rvations reveal a complex system consisting of a dense core, a rotatin g molecular disk around the infrared source IRS 7 and a dense, bipolar molecular outflow. The molecular disk is located close to the northea stern edge of the core and is obscured by outlying material from the f oreground core. The disk's radius is greater than 3 000 AU and its mas s is greater than 0.01 M.. The alignment, in the plane of the sky, bet ween the molecular disk's rotational axis and the extended NE-SW chain of Herbig-Haro objects in the vicinity is excellent. The mass of the central protostar IRS 7 is greater than 0.6 M.. The dense outflow corr esponds to the compact E-W directed outflow detected previously by Lev reault (1988). The Herbig Ae/Be star R CrA is eliminated as a candidat e driver for the dense, bipolar outflow. IRS 7 is the most likely driv er for this outflow, The ejection axes of the blue and redshifted lobe s of the bipolar outflow are substantially misaligned with respect to each other and with respect to the rotational axis of the molecular di sk. The masses and momenta of the red and blueshifted components of th e bipolar outflow are very well balanced with representative values be ing 0.06 M. and 0.22 M. km s(-1) respectively. The observations exclud e centrifugal acceleration of material from the molecular disk as the driving mechanism and source for the outflow. There is evidence of int eraction between the disk/outflow system and the dense foreground core : the approaching flow collides with the outer regions of the core cau sing a powerful shock which is manifest as SiO(J = 2 - 1, v = O) emiss ion and the Herbig-Haro objects HH 104 A and B. In addition, a bridge of redshifted material extends from the foreground core to the recedin g side of the molecular disk, We suggest that this feature represents an accretion stream feeding the molecular disk.