|4th of August 2017|
|Cosmic water fountains|
|by Pérez-Sánchez et al.|
Some giant stars (which, as they have evolved beyond
the asymptotic giant branch (AGB) region of the Hertzsprung–Russell diagram,
are referred to as post-asymptotic giant branch (post-AGB) stars)
form large bipolar structures in their surrounding circumstellar envelopes (CSEs).
These structures can be traced by emission
from fast molecular outflows, however the mechanism
responsible for the launching and collimation these outlflows is not clear.
When water vapour is detected in the molecular outflows, the stars are
referred to as water fountains.
A project to study these objects has been undertaken by
a team using data from three telescope facilities: the Karl G. Jansky Very Large Array (JVLA),
the Australia Telescope Compact Array (ATCA), and the Very Large Telescope (SINFONI-VLT).
Pérez-Sánchez et al.
report the results of the observations toward the water-fountain IRAS 18043-2116.
The image above shows the ATCA spectrum of this source around the 22 GHz water vapour line.
A total of 33 water vapour maser features were identified, where the size of the circle
shows the strength of the feature. The spectral features are spread over a velocity
range of 400 km/s -- indicating that this is a high speed fountain!
The results and interpretation of the observations are presented in Pérez-Sánchez et al., Astronomy & Astrophysics, 601, A68.