Deep into the Water Fountains

The case of IRAS 18043−2116

¹ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago, Chile
e-mail: aperezsa@eso.org
² Instituto de Radioastronomía y Astrofísica, UNAM, Apdo. Postal 3-72 (Xangari) 58089 Morelia, Michoacán, Mexico
³ Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
⁴ Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland

Received: 16 December 2016
Accepted: 15 February 2017

Abstract

Context. The formation of large-scale (hundreds to a few thousands of AU) bipolar structures in the circumstellar envelopes (CSEs) of post-asymptotic giant branch (post-AGB) stars is poorly understood. The shape of these structures, which is traced by emission from fast molecular outflows, suggests that the dynamics at the innermost regions of these CSEs does not depend only on the energy of the radiation field of the central star.

Aims. Multi-frequency observations toward a group of post-AGB sources known as Water Fountain (WF) nebulae can help to constrain the nature of the mechanism responsible for the launching and collimation of the fast molecular outlflows traced by high-velocity features of H₂O maser emission.

Methods. Deep into the WFs is an observational project based on the results of programs carried out with three telescope facilities: the Karl G. Jansky Very Large Array (JVLA), the Australia Telescope Compact Array (ATCA), and the Very Large Telescope (SINFONI-VLT).

Results. Here we report the results of the observations toward the WF nebula IRAS 18043−2116: detection of radio continuum emission in the frequency range 1.5–8.0 GHz, H₂O maser spectral features and radio continuum emission detected at 22 GHz, and H₂ ro-vibrational emission lines detected at the near infrared.

Conclusions. The high-velocity H₂O maser spectral features and the shock-excited H₂ emission could be produced in molecular layers that are swept up as a consequence of the propagation of a jet-driven wind. Using the derived H₂ column density, we estimated a molecular mass-loss rate on the order of 10^-9 M_⊙ yr^-1. On the other hand, if the radio continuum flux is generated as a consequence of the propagation of a thermal radio jet, the mass-loss rate associated with the outflowing ionized material is on the order of 10^-5 M_⊙ yr^-1. A rotating disk could be a plausible explanation for the mass-loss rates we estimated.