next up previous contents
Next: The pointing of Up: Scientific Results Previous: Scientific Results

A precessing jet in the L 1157 molecular outflow

F. Gueth, S. Guilloteau, R. Bachiller
Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, F-38406 Saint Martin d'Hères, France
Centro Astronómico de Yebes, Apartado 148, E-19080 Guadalajara, Spain
Abstract: The blue-shifted lobe of the L 1157 molecular outflow has been imaged in the CO J=1-0 line, and in the 2.6 mm continuum, with angular resolution of ( 7 pc at the distance of L 1157, 440 pc) at the IRAM interferometer. The data consist of a mosaic of 10 partially overlapping fields, complemented with short spacing information from the IRAM 30-m telescope.

The images reveal the presence of at least two prominent limb brightened cavities which have been likely created by the propagation of large bow shocks due to episodic events in a precessing, highly collimated jet. A simple spatio-kinematic model involving two different ejection events provides an accurate description of the observations. We find that the outflow is inclined by 80 to the line of sight, and that the axis of the underlying jet precesses on a cone of 6 opening angle, with a period of 4000 yr. We discuss the constraints derived from the present observations on several recent models for jet driven molecular outflows. We conclude that, similarly to what happens in other outflows (e.g.: L1448), the large opening angle of the L 1157 CO outflow is originated by the large size of the propagating bow shocks, since the precession in L 1157 happens in a narrow cone. However, the observed shape of the cavities evacuated by the bow shock propagation are not well accounted for by current models of gas entrainment by bow shocks.

Robert Lucas
Mon Sep 18 09:50:01 METDST 1995