From the ashes: JVLA observations of water fountain nebula candidates show the rebirth of IRAS 18455+0448

Abstract

Context. The class of water fountain nebulae is thought to represent the stage of the earliest onset of collimated bipolar outflows during the post-asymptotic giant branch phase. They thus play a crucial role in the study of the formation of bipolar planetary nebulae (PNe). To date, 14 water fountain nebulae have been identified. The identification of more sources in this unique stage of stellar evolution will enable us to study the origin of bipolar PNe morphologies in more detail. Aims. Water fountain candidates can be identified based on the often double peaked 22 GHz H 2 O maser spectrum with a large separation between the maser peaks (often >100 km s −1 ). However, even a fast bipolar outflow will only have a moderate velocity extent in its maser spectrum when located close to the plane of the sky. In this project we aim to enhance the water fountain sample by identifying objects whose jets are aligned close to the plane of the sky. Methods. We present the results of seven sources observed with the Jansky Very Large Array (JVLA) that were identified as water fountain candidates in an Effelsberg 100 m telescope survey of 74 AGB and early post-AGB stars. Results. We find that our sample of water fountain candidates displays strong variability in their 22 GHz H 2 O maser spectra. The JVLA observations show an extended bipolar H 2 O maser outflow for one source, the OH/IR star IRAS 18455+0448. This source was previously classified as a dying OH/IR star based on the exponential decrease of its 1612 MHz OH maser and the lack of H 2 O masers. We therefore also re-observed the 1612, 1665, and 1667 MHz OH masers. We confirm that the 1612 MHz masers have not reappeared and find that the1665/1667 MHz masers have decreased in strength by several orders of magnitude during the last decade. The JVLA observations also reveal a striking asymmetry in the red-shifted maser emission of IRAS 19422+3506. Conclusions. The OH/IR star IRAS 18455+0448 is confirmed to be a new addition to the class of water fountain nebulae. Its kinematic age is ∼70 yr, but could be lower, depending on the distance and inclination. Previous observations indicate, with significant uncertainty, that IRAS 18455+0448 has a surprisingly low mass compared to available estimates for other water fountain nebulae. The available historical OH maser observations make IRAS 18455+0448 unique for the study of water fountain nebulae and the launch of post-AGB bipolar outflows. The other candidate sources appear high mass-loss OH/IR stars with partly radially beamed H 2 O masers.

Interferometric confirmation of ‘water fountain’ candidates

“…Using a wider bandwidth, (Gómez et al 1994) also detected an additional high-velocity blueshifted component at 10 km s −1 , giving a separation of ≃ 70 km s −1 between both components, suggesting that this source was a WF candidate. However, later single-dish (Kim et al 2010;Vlemmings et al 2014) and interferometric observations (Gómez et al 1994;Vlemmings et al 2014) failed to detect any high-velocity emission and, in particular, the blueshifted component at 10 km s −1 was absent.…”

The jet feedback mechanism (JFM) in stars, galaxies and clusters

“…Many new observations and theoretical studies since the turn of the Millennium further consolidated the jet-shaping scenario of many PNe (e.g., Parthasarathy et al 2000;Bujarrabal et al 2001;Miranda et al 2001;Corradi et al 2001b;Guerrero et al 2001;Imai et al 2002;Riera et al 2003;Vinković et al 2004;Huggins et al 2004;Peña et al 2004;Balick & Hajian 2004;Arrieta et al 2005;Oppenheimer et al 2005;Sahai et al 2005;Vlemmings et al 2006;Miranda et al 2010;Nakashima et al 2010;Phillips et al 2010;Sahai et al 2011;Szyszka et al 2011;López et al 2012;Clark et al 2013;Pérez-Sánchez et al 2013;Vlemmings et al 2014;Fang et al 2015 Dennis et al 2008Dennis et al , 2009Lee et al 2009;Huarte-Espinosa et al 2012;Velázquez et al 2012;Balick et al 2013;Velázquez et al 2014 for theoretical studies; these papers composed a small fraction of the papers studying jets in PNe). X-ray observations seem also to support the presence of jet-inflated bubbles and of jets Sahai et al 2003), similar to X-ray jets in symbiotic systems (e.g., Kellogg et al 2001;Galloway & Sokoloski 2004).…”

“…Many new observations and theoretical studies since the turn of the Millennium further consolidated the jet-shaping scenario of many PNe (e.g., Parthasarathy et al 2000;Bujarrabal et al 2001;Miranda et al 2001;Corradi et al 2001b;Guerrero et al 2001;Imai et al 2002;Riera et al 2003;Vinković et al 2004;Huggins et al 2004;Peña et al 2004;Balick & Hajian 2004;Arrieta et al 2005;Oppenheimer et al 2005;Sahai et al 2005;Vlemmings et al 2006;Miranda et al 2010;Nakashima et al 2010;Phillips et al 2010;Sahai et al 2011;Szyszka et al 2011;López et al 2012;Clark et al 2013;Pérez-Sánchez et al 2013;Vlemmings et al 2014;Fang et al 2015;Gómez-Muñoz et al 2015;Akras & Gonçalves 2016;Clyne et al 2015;Danehkar 2015;Danehkar et al 2016, for observational papers, and, e.g., Soker & Rappaport 2000Blackman et al 2001;Livio & Soker 2001;Soker 2002;García-Arredondo & Frank 2004;Velázquez et al 2004Velázquez et al , 2007Riera et al 2005;Raga et al 2008;Stute & Sahai 2007;…”

The First “Water Fountain” Collimated Outflow in a Planetary Nebula

“…Only 16 sources have been identified so far as possible WFs (Desmurs 2012;Vlemmings et al 2014). Fourteen of them seem to be in the post-AGB phase.…”