High velocity precessing jets from the water fountain IRAS18286-0959 revealed by very long baseline array observations

Abstract

We report the results of multi-epoch Very Long Baseline Array observations of the 22.2GHz H 2O maser emission associated with the "water fountain" IRAS18286-0959. We suggest that this object is the second example of a highly collimated bipolar precessing outflow traced by H 2O maser emission, the other is W43A. The detected H 2O emission peaks are distributed over a velocity range from -50kms -1 to 150kms -1. The spatial distribution of over 70% of the identified maser features is found to be highly collimated along a spiral jet (jet 1) extended southeast to northwest; the remaining features appear to trace another spiral jet (jet 2) with a different orientation. The two jets form a "double-helix" pattern which lies across ∼200 mas. The maser distribution is reasonably fit by a model consisting of two bipolar precessing jets. The three-dimensional velocities of jet 1 and jet 2 are derived to be 138kms -1 and 99kms -1, respectively. The precession period of jet 1 is about 56 years. For jet 2, three possible models are tested and they give different values for the kinematic parameters. We propose that the appearance of two jets is the result of a single driving source with significant proper motion. © 2011. The American Astronomical Society. All rights reserved.