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Astron. Astrophys. 321, 575-590 (1997)

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A molecular disk and dense outflow in Corona Australis *

I.M. Anderson 1, J. Harju 1, L.B.G. Knee 2, 3 and L.K. Haikala 1, 2

1 Observatory, P.O. Box 14, FIN-00014 University of Helsinki, Finland
2 Swedish-ESO Submillimetre Telescope, European Southern Observatory, Casilla 19001 Santiago 19, Chile
3 Dominion Radio Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council of Canada, P.O. Box 248, Penticton, BC, V2A 6K3, Canada

Received 10 July 1996 / Accepted 19 July 1996

Abstract

The central region of the molecular outflow in the R Coronae Australis cloud was mapped in [FORMULA], H13 [FORMULA], [FORMULA] and C18 O [FORMULA] with the SEST. In addition to the maps, selected positions were observed in SiO([FORMULA]). The observations reveal a complex system consisting of a dense core, a rotating molecular disk around the infrared source IRS 7 and a dense, bipolar molecular outflow. The molecular disk is located close to the northeastern edge of the core and is obscured by outlying material from the foreground core. The disk's radius is greater than 3 000 AU and its mass is greater than 0.01  [FORMULA]. The alignment, in the plane of the sky, between 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  [FORMULA]. The dense outflow corresponds to the compact E-W directed outflow detected previously by Levreault (1988). The Herbig Ae/Be star R CrA is eliminated as a candidate driver for the dense, bipolar outflow. IRS 7 is the most likely driver for this outflow. The ejection axes of the blue and redshifted lobes of the bipolar outflow are substantially misaligned with respect to each other and with respect to the rotational axis of the molecular disk. The masses and momenta of the red and blueshifted components of the bipolar outflow are very well balanced with representative values being 0.06  [FORMULA] and 0.22  [FORMULA] km s-1 respectively. The observations exclude centrifugal acceleration of material from the molecular disk as the driving mechanism and source for the outflow. There is evidence of interaction between the disk/outflow system and the dense foreground core: the approaching flow collides with the outer regions of the core causing a powerful shock which is manifest as SiO [FORMULA] emission and the Herbig-Haro objects HH104 A and B. In addition, a bridge of redshifted material extends from the foreground core to the receding side of the molecular disk. We suggest that this feature represents an accretion stream feeding the molecular disk.

Key words: stars: formation – ISM: individual – R CrA-clouds – ISM: jets and outflows – ISM: kinematics and dynamics – ISM: molecules – radio lines: ISM

* Based on observations collected at the European Southern Observatory, La Silla, Chile

Send offprint requests to: Moray Anderson (moray@ceres.helsinki.fi)

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998
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