Volume 578, June 2015
|Number of page(s)||15|
|Section||Stellar structure and evolution|
|Published online||15 June 2015|
A search for water maser emission toward obscured post-AGB star and planetary nebula candidates⋆
1 Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
2 Centro de Astrobiología, INTA-CSIC, Carretera M-108, km. 4, 28850 Torrejón de Ardoz, Madrid, Spain
3 UMR 6525 H.Fizeau, Université de Nice Sophia Antipolis, CNRS, OCA. Parc Valrose, 06108 Nice Cedex 2, France
4 Centro de Radioastronomía y Astrofísica, UNAM, Campus Morelia, Apdo. Postal 3-72, Morelia, 58089 Michoacán, Mexico
5 Instituto de Astronomía y Meteorología, CUCEI, Universidad de Guadalajara, Av. Vallarta No. 2602, Col. Arcos Vallarta, 44130 Guadalajara, Jalisco, Mexico
6 Institut de Ciències de l’Espai (CSIC)/IEEC, 08034 Barcelona, Spain
7 Institut de Ciències del Cosmos, Universitat de Barcelona (associated unit of CSIC through the ICE), Martí i Franquès 1, 08028 Barcelona, Spain
Received: 3 March 2015
Accepted: 17 April 2015
Context. Water maser emission at 22 GHz is a useful probe for studying the transition between the nearly spherical mass loss in the asymptotic giant branch (AGB) to a collimated one in the post-AGB phase. In their turn, collimated jets in the post-AGB phase could determine the shape of planetary nebulae once photoionization starts.
Aims. We intend to find new cases of post-AGB stars and planetary nebulae (PNe) with water maser emission, including some especially interesting and rare types: water fountains (evolved objects with high velocity collimated jets traced by water masers) or water-maser-emitting PNe. Since previous studies have shown a higher detection rate of water maser emission in evolved objects that are optically obscured, we selected a sample that contains a significant fraction of post-AGB and young PN candidate sources showing signs of strong obscuration.
Methods. We searched for water maser emission in 133 evolved objects using the radio telescopes in Robledo de Chavela, Parkes, and Green Bank.
Results. We detected water maser emission in 15 sources of our sample, of which seven are reported here for the first time (IRAS 13483−5905, IRAS 14249−5310, IRAS 15408−5413, IRAS 17021−3109, IRAS 17348−2906, IRAS 17393−2727, and IRAS 18361−1203). We identified three water fountain candidates: IRAS 17291−2147, with a total velocity spread of ≃96 km s-1 in its water maser components and two sources (IRAS 17021−3109 and IRAS 17348−2906) that show water maser emission whose velocity lies outside the velocity range covered by OH masers. We have also identified IRAS 17393−2727 as a possible new water-maser-emitting PN.
Conclusions. The detection rate is higher in obscured objects (14%) than in those with optical counterparts (7%), which is consistent with previous results. Water maser emission seems to be common in objects that are bipolar in the near-IR (43% detection rate in such sources). The water maser spectra of water fountain candidates like IRAS 17291−2147 show significantly fewer maser components than others (e.g., IRAS 18113−2503). We speculate that most post-AGBs may show water maser emission with wide enough velocity spread (≥100 km s-1) when observed with enough sensitivity and/or for long enough periods of time. Therefore, it may be necessary to single out a special group of “water fountains”, probably defined by their high maser luminosities. We also suggest that the presence of both water and OH masers in a PN is a better tracer of its youth, than is the presence of just one of these species.
Key words: masers / surveys / stars: AGB and post-AGB / stars: mass-loss / planetary nebulae: general
Table 1 and Fig. 1 are available in electronic form at http://www.aanda.org
© ESO, 2015
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