Stellar water fountains: planetary nebulae in the making

Planetary nebulae (PN) are one of the final phases in the evolution of
low and intermediate mass stars (<8 Msun). They display a great variety
of shapes, although in their previous phases (Asymptotic giant branch
=AGB) they have a spherical geometry. The transition from spherical
symmetry to asymmetry must occur during the short post-AGB phase or in
the early PN phase. Here we present a special type of evolved stars,
called "water fountains". They are  characterized by high-velocity jets 
traced by water masers at radio wavelengths. This phenomenon seems to
occur mostly in the post-AGB phase. These jets have short dynamical
ages (<100 years) and may be one of the first manifestations of
collimated mass loss in evolved stars, and a possible agent to break
their spherical symmetry. We will review the status of our knowledge
on water fountains, including the search for new candidates, the
characterization of their physical properties, and their possible role
on PN shaping.
05/12/2013 - 13:30
Dr. JFrancisco Gómez