Rapidly Evolving Episodic Outflow in the Fastest Water Fountain

2019-10-04
12:15
CSIC
Sala Alberto Lobo (ICE building, UAB Campus)
Rapidly Evolving Episodic Outflow in the Fastest Water Fountain
Water fountains (WF) are evolved stars showing early stages of collimated mass-loss during transition from the asymptotic giant branch, providing valuable insight into the formation of asymmetric planetary nebulae. 

We present the results of our Very Long Baseline Interferometry (VLBI) water maser observations, which determine the spatial and three-dimensional kinematic structure of the masers associated with the fastest WF IRAS 18113−2503. The water masers trace three pairs of high-velocity (~150-300 km/s) bipolar bow shocks on a scale of ~0.18 arcsec (~2000 AU).

The expansion velocities of the bow shocks exhibit an exponential decrease as a function of distance from the central star, which can be explained by an episodic, jet-driven outflow decelerating due to drag forces in a circumstellar envelope. We estimate an initial ejection velocity of ~840 km/s, and a period for the ejections of 10-20 yr, with the youngest being ~12 yr old. We hypothesize that IRAS 18113−2503 hosts a binary central star with a separation of ~10 AU. We also explain the water maser monitoring program we are currently doing on this WF for testing some of our observational predictions.

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