The kinematics of water masers in the stellar molecular outflow source, IRAS 19134+2131

¹ Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, The Netherlands e-mail: imai@jive.nl
² Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1562, USA e-mail: morris@astro.ucla.edu
³ Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109, USA e-mail: Raghvendra.Sahai@jpl.nasa.gov
⁴ Departamento de Astronomía, Universitat de Valéncia, 46100 Burjassot, Spain e-mail: kazuya.hachisuka@uv.es
⁵ Instituto de Astrofísica de Canarias, La Laguna, Tenerife 38200, Spain e-mail: jraf@cca.iac.es

Corresponding author: H. Imai, hiroimai@sci.kagoshima-u.ac.jp

Received: 12 November 2003
Accepted: 4 March 2004

Abstract

Using the Very Large Array (VLA) and the Very Long Baseline Array (VLBA), we have observed water maser emission in the proto-planetary nebula candidate IRAS 19134+2131, in which the water maser spectrum has two groups of emission features separated in radial velocity by ~100 km s^-1. The blue-shifted and red-shifted clusters of maser features are clearly separated spatially by ~150 mas, indicative of a fast collimated flow. However, not all of the maser features are aligned along the axis of the flow, as is seen in the similar high-velocity water maser source, W43A. Comparing the VLA and VLBA maps of the water maser source, we find 4 maser features that were active for 2 years. Using only VLBA data, we identified proper motions for 8 maser features. The full 3D outflow velocity is estimated to be ~130 km s^-1, indicating that the dynamical age of the flow is only ~50 yr. On the basis of the relative positions with respect to the nearby extragalactic reference source, J1925+2106, we also obtain a secular motion of IRAS 19134+2131of  mas yr^-1 along the Galactic plane toward the Galactic centre. This indicates a “far distance" (≥16 kpc) for IRAS 19134+2131 if the Galactic rotation curve remains flat at 220 km s^-1.