2004ApJ...601..921D

We report on a water maser survey toward a sample of 27 planetary nebulae (PNe) using the Robledo de Chavela and Medicina single-dish antennas, as well as the Very Large Array (VLA). Two detections have been obtained: the already known water maser emission in K3-35, and a new cluster of masers in IRAS 17347-3139. This low rate of detections is compatible with the short lifetime of water molecules in PNe (∼100 yr). The water maser cluster at IRAS 17347-3139 are distributed on a ellipse of size ≃0".2x0".1, spatially associated with compact 1.3 cm continuum emission (simultaneously observed with the VLA). From archive VLA continuum data at 4.9, 8.4, and 14.9 GHz, a spectral index α=0.76±0.03 (S_ν∝ν^α) is derived for this radio source, which is consistent with either a partially optically thick ionized region or an ionized wind. However, the latter scenario can be ruled out by mass-loss considerations, thus indicating that this source is probably a young PN. The spatial distribution and the radial velocities of the water masers are suggestive of a rotating and expanding maser ring, tracing the innermost regions of a torus formed at the end of the asymptotic giant branch phase. Given that the 1.3 cm continuum emission peak is located near one of the tips of the major axis of the ellipse of masers, we speculate on a possible binary nature of IRAS 17347-3139, where the radio continuum emission could belong to one of the components and the water masers would be associated with a companion.