A search for water maser emission toward obscured post-AGB star and planetary nebula candidates

Abstract

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 watermaser-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.

Unusual Shock-Excited Oh Maser Emission in a Young Planetary Nebula

“…Uscanga et al (2012) find the sizes and optical visibilities of the maser-associated PNe suggest a range of ages, but it is possible that the subgroup of PNe showing both OH and H 2 O are among the youngest PNe known (Gómez et al 2015). Our observations confirm IRAS 16333−4807 as a member of this rare group of potentially young PNe.…”

“…The presence of maser emission (OH or H 2 O) in a PN is usually considered to be a sign of its youth, since these masers are expected to disappear shortly after the end of the AGB phase (Gómez et al 1990). Uscanga et al (2012) find the sizes and optical visibilities of the maser-associated PNe suggest a range of ages, but it is possible that the subgroup of PNe showing both OH and H 2 O are among the youngest PNe known (Gómez et al 2015). Our observations confirm IRAS 16333−4807 as a member of this rare group of potentially young PNe.…”

“…Our observations confirm IRAS 16333−4807 as a member of this rare group of potentially young PNe. So far, in addition to IRAS 16333−4807, only K 3−35 (Miranda et al 2001), IRAS 17347−3139 (de Gregorio-Monsalvo et al 2004Tafoya et al 2009), and possibly IRAS 17347−3139 (Gómez et al 2015) show maser emission from both molecules.…”

Vertical distribution and kinematics of protoplanetary nebulae in the galaxy

“…However, at the post-AGB phase, apart from a more or less symmetric shell, collimated high velocity bipolar jets are observed in the radio band (Pérez-Sánchez et al 2013). The environment in the shells and jets is favorable for the emergence of maser emission (Gómez et al 2015). Highly accurate measurements of the trigonometric parallaxes have already been performed with ground-based very-long baseline interferometers for some post-AGB objects (Imai et al 2007(Imai et al , 2013.…”

Looking for new water-fountain stars

“…There remain several sources that are considered to be WF candidates based on singledish observations (Yung et al 2013, 2014, Gómez et al 2015. Despite showing larger velocities in their H 2 O maser spectrum than in OH, the velocity spread of some of these candidates is relatively low ( 40 km s −1 ), compared with the case of some WFs (> 100 km s −1 ).…”