Kinematics of the H2O masers at the centre of the PN K3-35

TL;DR

This study analyzes water maser kinematics at the center of planetary nebula K3-35, revealing a rotating and expanding ring structure that may influence jet collimation.

Contribution

It provides the first detailed kinematic model of water masers in K3-35, identifying a rotating and expanding ring structure with specific velocity and orientation.

Findings

Masers trace a ~100 AU ring with 55° inclination.

Ring exhibits 1.4 km/s expansion and 3.1 km/s rotation.

Ring orientation is nearly orthogonal to the jet direction.

Abstract

We have studied the kinematics traced by the water masers located at the centre of the planetary nebula (PN) K3-35, using data from previous Very Large Array (VLA) observations. An analysis of the spatial distribution and line-of-sight velocities of the maser spots allows us to identify typical patterns of a rotating and expanding ring in the position-velocity diagrams, according to our kinematical model. We find that the distribution of the masers is compatible with tracing a circular ring with a ~0.021 arcsec (~100 AU) radius, observed with an inclination angle with respect to the line of sight of 55 degrees. We derive expansion and rotation velocities of 1.4 and 3.1 km/s, respectively. The orientation of the ring projected on the plane of the sky, at PA 158 degrees, is almost orthogonal to the direction of the innermost region of the jet observed in K3-35, suggesting the presence of a disc or torus that may be related to the collimation of the outflow.