High Velocity Precessing Jets from the Water Fountain IRAS 18286-0959 Revealed by VLBA Observations

TL;DR

This study uses VLBA observations to reveal a double-helix precessing jet structure in the water fountain IRAS 18286-0959, providing insights into bipolar outflows in evolved stars.

Contribution

It presents the first detailed model of two precessing bipolar jets in IRAS 18286-0959, suggesting a single driving source with proper motion.

Findings

Two collimated spiral jets form a double-helix pattern.

Jet velocities are approximately 138 km/s and 99 km/s.

Precession period of jet 1 is about 56 years.

Abstract

We report the results of multi-epoch VLBA observations of the 22.2GHz water maser emission associated with the "water fountain" IRAS 18286-0959. We suggest that this object is the second example of a highly collimated bipolar precessing outflow traced by water maser emission, the other is W43A. The detected water emission peaks are distributed over a velocity range from -50km/s to 150km/s. 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 milliarcseconds. The maser distribution is reasonably fit by a model consisting of two bipolar precessing jets. The 3D velocities of jet 1 and jet 2 are derived to be 138km/s and 99km/s, 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.