New detections of H2O masers in planetary nebulae and post-AGB stars using the Robledo-70m antenna

摘要

Aims: We investigated the possible relationship between the evolutionarystage of post-AGB stars and planetary nebulae (PNe) and the presence of watermasers in their envelopes. Methods: We have used NASA's 70-m antenna in Robledo de Chavela (Spain) tosearch for the water maser transition at 22235.08 MHz, towards a sample of 105sources with IRAS colour characteristic of post-AGB stars and PNe atdeclination >-32 deg. 83% of the sources in the sample are post-AGB stars, 15%PNe or PN candidates, while only 2% seem to be HII regions. Results: We have detected five water masers, of which four are reported forthe first time: two in PNe (IRAS 17443-2949 and IRAS 18061-2505), a ``waterfountain'' in a post-AGB star (IRAS 16552-3050), and one in a source previouslycatalogued as a PN, but whose classification is uncertain (IRAS 17580-3111). Conclusions: The unexpected detections of water masers in two objects amongthe small subset of PNe led us to suggest that the PNe harbouring water masersare a special type of massive, rapidly evolving PNe.