Deep into the Water Fountains

Abstract

Context. The formation of large-scale (hundreds to 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, 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 towards a group of post-AGB sources known as Water Fountain 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 H 2 O maser emission. Methods. Deep into the Water Fountains 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 towards the WF nebula IRAS 18043−2116: Detection of radio continuum emission in the frequency range 1.5 GHz -8.0 GHz; H 2 O maser spectral features and radio continuum emission detected at 22 GHz, and H 2 ro-vibrational emission lines detected at the near infrared. Conclusions. The high-velocity H 2 O maser spectral features, and the shock-excited H 2 emission detected could be produced in molecular layers which are swept up as a consequence of the propagation of a jet-driven wind. Using the derived H 2 column density, we estimated a molecular mass-loss rate of the order of 10 −9 M yr −1 . On the other hand, if the radio continuum flux detected is generated as a consequence of the propagation of a thermal radio jet, the mass-loss rate associated to the outflowing ionized material is of the order of 10 −5 M yr −1 . The presence of a rotating disk could be a plausible explanation for the mass-loss rates estimated.

Searching for nascent planetary nebulae: OHPNe candidates in the SPLASH survey

“…From our SPLASH-ATCA data, we obtain a flux density of 0.9 mJy at 2.1 GHz, although the image is heavily contaminated by sidelobes from other sources in the field. A more reliable value of 0.6 mJy at 2 GHz was obtained by Pérez-Sánchez et al (2017). These authors also showed that the spectral index of the radio continuum emission is consistent with free-free emission from an ionized jet.…”

“…and continuum emission (within 5 ), even if the maser might be associated with an evolved star, but a literature search showed that the continuum emission traces an extragalactic object. We also detect IRAS 18043-2116, a WF post-AGB star (Walsh et al 2009), whose radio continuum emission has been studied by Pérez-Sánchez et al (2017). The remaining sources with a positive match, are reported in Table 2.…”

Submillimeter H2O maser emission from water fountain nebulae

“…According to the model proposed by Elitzur et al (1989), when the shocked material cools down, H 2 and H 2 O molecules form in gas that is maintained at T k =400 K. As mentioned above, for this temperature the luminosity ratio L p (22 GHz)/L p (321 GHz) is expected to be 5. Comparing the intensities of the 22 GHz masers (see Deacon et al 2007;Walsh et al 2009;Yung et al 2011;Pérez-Sánchez et al 2017) and the 321 GHz masers of IRAS 18043−2116 and IRAS 18286−0959, we find a luminosity ratio ≈1. This implies a kinetic temperature T k >1000 K for the gas (Neufeld & Melnick 1990;Yates et al 1997).…”

Accurate OH Maser Positions from the SPLASH Survey. III. The Final 96 deg2

“…Furthermore, this source is also a water fountain source with the water maser emission distributed over a velocity spread of nearly 400 km s −1 (Walsh et al 2009). Pérez-Sánchez et al (2017) also detected the radio continuum emission toward this source, which could arise from a thermal radio jet. In the GLIMIPSE three-color image, this star is very bright at 8 µm.…”