Related papers: Low- and high-velocity `water fountains': differen…

Water fountain stars (WFs) are evolved objects with water masers tracing high-velocity jets (up to several hundreds of km s$^{-1}$). They could represent one of the first manifestations of collimated mass-loss in evolved objects and thus,…

"Water fountains" (WFs) are evolved objects showing high-velocity, collimated jets traced by water maser emission. Most of them are in the post-Asymptotic Giant Branch and they may represent one of the first manifestations of collimated…

Water fountains (WFs) are thought to be objects in the morphological evolution of the circumstellar envelopes of low- and intermediate-mass evolved stars, transitioning from spherically symmetric to asymmetric shapes. We used databases of…

Water fountain stars represent a stage between the asymptotic giant branch (AGB) and planetary nebulae phases, when the mass loss changes from spherical to bipolar. These types of evolved objects are characterized by high-velocity jets in…

[abridged] 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…

Water maser emission at 22 GHz is a useful probe to study the transition between the nearly spherical mass-loss in the AGB to a collimated one in the post-AGB phase. In their turn, collimated jets in the post-AGB phase could determine the…

Stars like the Sun expel their outer layers and form planetary nebulae (PNe) as they evolve into white dwarfs. PNe exhibit diverse morphologies, the origins of which are not fully understood. PNe with OH (OHPNe) and H$_{2}$O (H$_{2}$OPNe)…

Aims: We investigated the possible relationship between the evolutionary stage of post-AGB stars and planetary nebulae (PNe) and the presence of water masers in their envelopes. Methods: We have used NASA's 70-m antenna in Robledo de…

We present the results of a 22GHz H2O maser survey toward a new sample of AGB and post-AGB star candidates. Most of the objects are selected for the first time based on the AKARI data, which have high flux sensitivity in the mid-infrared…

(Abridged) 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…

Water fountain objects are generally defined as "evolved stars with low to intermediate initial mass accompanied by high-velocity molecular jets detectable in the 22.235 GHz H$_2$O maser line". They are the key objects of understanding the…

We present Very Large Array (VLA) observations of H2O and OH masers, as well as radio continuum emission at 1.3 and 18 cm toward three sources previously cataloged as planetary nebulae (PNe) and in which single-dish detections of H2O masers…

Some evolved stars in the pre-planetary nebula phase produce highly-collimated molecular outflows that resemble the accretion-driven jets and outflows from pre-main sequence stars. We show that IRAS 16342-3814 (the Water Fountain Nebula) is…

We report the first detection of submillimeter water maser emission toward water-fountain nebulae, which are post-AGB stars that exhibit high-velocity water masers. Using APEX we found emission in the ortho-H2O (10_29-9_36) transition at…

We report on the results of two epochs of Very Long Baseline Array (VLBA) observations of the 22 GHz water masers toward IRAS 19190+1102. The water maser emission from this object shows two main arc-shaped formations perpendicular to their…

We intended to study the incidence and characteristics of water masers in the envelopes of stars in the post-AGB and PN evolutionary stages. We have used the 64-m antenna in Parkes (Australia) to search for water maser emission at 22 GHz,…

Many aspects of the evolutionary phase in which Asymptotic Giant Branch stars (AGB stars) are in transition to become Planetary Nebulae (PNe) are still poorly understood. An important question is how the circumstellar envelopes of AGB stars…

[Context] Water fountain stars are very young post-AGB stars with high velocity water maser jets. They are the best objects to study the onset of bipolar jets from evolved stars due to their young dynamical ages. [Methods] We use the…

We investigated whether "velocity excess" in circumstellar maser lines can diagnose the earliest evolutionary phases of Water Fountains (WFs). Here we define "velocity excess" as maser emission (e.g., H$_2$O 22.235 GHz or OH 1665/1667 MHz)…

We present 2 to 2.4 micron integral field spectroscopy of a sample of hot post-AGB stars with early-B spectral types, using the NIFS instrument on Gemini North. These stars are just beginning to ionize their immediate environments and turn…