Sensitive CO and 13CO survey of water fountain stars. Detections towards IRAS 18460-0151 and IRAS 18596+0315

Abstract

Water fountain stars represent a stage between the asymptotic giant branch (AGB) and planetary nebulae phases, when the mass loss changes from spherical to bipolar. These types of evolved objects are characterized by high-velocity jets in the 22 GHz water maser emission. We surveyed the CO and 13CO line emission towards a sample of ten water fountain stars through observing the J=1-0 and 2-1 lines of CO and 13CO, using the 30m IRAM radio telescope at Pico Veleta. All the water fountains visible from the observatory were surveyed. Most of the line emission arises from foreground or background Galactic clouds, and we had to thoroughly analyse the spectra to unveil the velocity components related to the stars. In two sources, IRAS 18460-0151 and IRAS 18596+0315, we identified wide velocity components with a width of 35-40 km/s that are centred at the stellar velocities. These wide components can be associated with the former AGB envelope of the progenitor star. A third case, IRAS 18286-0959, is reported as tentative; in this case a pair of narrow velocity components, symmetrically located with respect to the stellar velocity, has been discovered. We also modelled the line emission using an LVG code and derived some global physical parameters, which allowed us to discuss the possible origin of this gas in relation to the known bipolar outflows. For IRAS 18460-0151 and IRAS 18596+0315, we derived molecular masses close to 0.2 solar masses, mean densities of 10^4 cm^{-3}, and mass-loss rates of 10^{-4} M_sun/yr. The kinetic temperatures are rather low, between 10 and 50 K in both cases, which suggests that the CO emission is arising from the outer and cooler regions of the envelopes. No fitting was possible for IRAS 18286-0959, because line contamination can not be discarded in this case.

13 pages, 9 figures, accepted to Astronomy and Astrophysics

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Cited by in corpus (9)

• ALMA imaging of the nascent planetary nebula IRAS 15103-5754
• Observational identification of a sample of likely recent Common-Envelope Events
• Experimental demonstration of an inertial collimation mechanism in nested outflows
• The first "water fountain" collimated outflow in a planetary nebula
• Rapidly-evolving episodic outflow in IRAS 18113-2503: clues to the ejection mechanism of the fastest water fountain
• From the ashes: JVLA observations of water fountain nebula candidates show the rebirth of IRAS 18455+0448
• A search for water maser emission toward obscured post-AGB star and planetary nebula candidates
• Do Water Fountain Jets Really Indicate the Onset of the Morphological Metamorphosis of Circumstellar Envelopes?
• Searching for nascent planetary nebulae: OHPNe candidates in the SPLASH survey