Searching for nascent planetary nebulae: OHPNe candidates in the SPLASH survey

Abstract

The evolution of asymptotic giant branch stars from the spherical symmetry into the diverse shapes of planetary nebulae (PNe) is a topic of intensive research. Young PNe provide a unique opportunity to characterize the onset of this transitional phase. In particular, OH maser-emitting PNe (OHPNe) are considered nascent PNe. In fact, only 6 OHPNe have been confirmed to date. In order to identify and characterize more OHPNe, we processed the unpublished continuum data of the interferometric follow-up of the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH). We then matched the interferometric positions of OH maser and radio continuum emission, considering the latter as a possible tracer of free-free emission from photoionized gas, characteristic of PNe. We report 8 objects with a positive coincidence, 4 of which are classified as candidate OHPNe here for the first time (IRAS 16372-4808, IRAS 17494-2645, IRAS 18019-2216 and OH 341.6811+00.2634). Available evidence strongly indicates that they are evolved stars, while the comparison with confirmed OHPNe indicates that they are likely to be PNe. Their final confirmation as bona fide PNe, however, requires optical/infrared spectroscopy. The obtained spectral indices of the radio continuum emission (between $\simeq$ 0.4 - 1.3) are consistent with partially optically thick free-free emission from photoionized gas. Also, they cluster in the same region of a WISE colour-colour diagram as that of the confirmed OHPNe ($9.5\lesssim [3.4]-[22]\lesssim 13.5$, and $4.0\lesssim [4.6]-[12]\lesssim 7.0$), thus this diagram could help to identify more OHPNe candidates in the future.

17 pages, 7 figures, 5 tables. Accepted for publication in MNRAS

References in corpus (16)

• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• The WFCAM Science Archive
• The RMS Survey: Radio observations of candidate massive YSOs in the southern hemisphere
• Accurate water maser positions from HOPS
• H2O Maser Observations of Candidate Post-AGB Stars and Discovery of Three High-velocity Water Sources
• Kinematics of the H2O masers at the centre of the PN K3-35
• Radio interferometric observations of candidate water-maser-emitting planetary nebulae
• Stellar molecular jets traced by maser emission
• Observational identification of a sample of likely recent Common-Envelope Events
• Accurate OH maser positions from the SPLASH pilot region
• Time-variable non-thermal emission in the planetary nebula IRAS 15103-5754
• The first "water fountain" collimated outflow in a planetary nebula
• Accurate OH Maser Positions From The SPLASH Survey III: The Final 96 Square Degrees
• H${}_2$O maser emission associated with the planetary nebula IRAS 16333$-$4807
• Jet parameters for a diverse sample of jet-launching post-AGB binaries
• SPLASH: The Southern Parkes Large-Area Survey in Hydroxyl -- Data Description & Release

Cited by in corpus (1)

• Evolution of the outflow in the water fountain source IRAS 18043$-$2116