First detection of CO lines in a water fountain star

Abstract

Context. Water fountain stars are very young post-AGB stars with high velocity water maser jets. They are the best objects in which to study the onset of bipolar jets from evolved stars due to their young dynamical ages. However, none of them has been observed in any thermal lines. Aims. We aim to search for CO lines in the water fountain star IRAS 16342-3814 and investigate the properties of its thermal gas. Methods. The proximity, peculiar stellar velocity and high Galactic latitude of IRAS 16342-3814 make a single dish observation possible. We use the Arizona Radio Observatory 10 m telescope to observe the CO J = 2−1 line and compare the line parameters with those of masers. Results. We report the detection of 12 CO and 13 CO J = 2−1 lines from IRAS 16342-3814. The inferred 12 CO mass loss rate is an order of magnitude lower than the infrared and OH mass loss rates, indicating a very cold and thick O-rich circumstellar envelope around the star. We also find a 12 CO expansion velocity of V exp = 46 ± 1 km s −1 that is too high for an AGB wind and confirm the systemic velocity of 44 ± 1 km s −1 . In addition we measure a very low 12 CO/ 13 CO line ratio of 1.7. Conclusions. The first detection of CO lines has provided a new way to investigate water fountain stars. Given the high expansion velocity of the CO gas and its relation to maser velocities, we infer that the CO emission region is co-located with the OH mainline masers in the warm base of the optical bipolar lobes, while the high velocity OH 1612 MHz and H 2 O masers are located in the side walls and at the farthest ends of the bipolar lobes, respectively. Further observations are highly desirable to understand the very low 12 CO/ 13 CO line ratio.

From the ashes: JVLA observations of water fountain nebula candidates show the rebirth of IRAS 18455+0448

“…The applicability of the expansion velocity -main sequence mass relation, which yields this low mass, to individual sources is however highly uncertain. For example observations of CO and its isotopologues may provide further mass estimates (e.g., He et al 2008). Furthermore, Very Long Baseline Interferometry (VLBI) observations will be needed to derive a more accurate distance, and constrain internal kinematics.…”

Sensitive CO and13CO survey of water fountain stars

“…CO and 13 CO spectra have been widely observed in AGB and post-AGB stars; modelling them has been used to determine the mass-loss rate, the total mass, and other physical parameters (see, for example, Teyssier et al 2006). So far, IRAS 16342-3814 is the only WF where thermal line emission has been unambiguously reported (He et al 2008;Imai et al 2009). From the detection of the CO and (tentatively) 13 CO J = 2 → 1 lines, He et al (2008) have determined an expansion velocity of 46 km s −1 , higher than that expected in an AGB envelope (typically 15 km s −1 ).…”

“…So far, IRAS 16342-3814 is the only WF where thermal line emission has been unambiguously reported (He et al 2008;Imai et al 2009). From the detection of the CO and (tentatively) 13 CO J = 2 → 1 lines, He et al (2008) have determined an expansion velocity of 46 km s −1 , higher than that expected in an AGB envelope (typically 15 km s −1 ). Surprisingly, the CO J = 3 → 2 line reported recently (Imai et al 2012) shows a different kinematics, depicting an even broader profile (>200 km s −1 ).…”

Dust shell model of the water fountain source IRAS 16342–3814

“…He et al (2008) detected a low 12 CO/ 13 CO intensity ratio of 1.7 and concluded that 12 C is being converted into 13 C via the hot bottom burning process, suggesting that the initial mass of the central star is as high as > ∼ 5 M . Another characteristic of this object is high-velocity maser components.…”