First detection of CO lines in a water fountain star

TL;DR

This study reports the first detection of CO lines in a water fountain star, revealing a cold, thick circumstellar envelope and high expansion velocities, providing new insights into the early stages of bipolar jet formation in evolved stars.

Contribution

The paper presents the first detection of CO lines in a water fountain star, offering new methods to study the onset of bipolar jets in evolved stars.

Findings

Detected 12CO and 13CO J=2-1 lines in IRAS 16342-3814.

Found a high CO expansion velocity of 46 km/s.

Measured a very low 12CO/13CO line ratio of 1.7.

Abstract

[Context] Water fountain stars are very young post-AGB stars with high velocity water maser jets. They are the best objects to study the onset of bipolar jets from evolved stars due to their young dynamical ages. [Methods] We use the Arizona Radio Observatory 10m telescope to observe the CO J=2-1 line and compare the line parameters with that of masers. [Results] We report the detection of 12CO and 13COJ=2-1 lines from IRAS 16342-3814. The inferred 12CO 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 12CO expansion velocity of Vexp = 46 +- 1 km/s that is too high for an AGB wind and confirm the systemic velocity of 44 +- 1 km/s. In addition we measure a very low 12CO/13CO line ratio of 1.7. [Conclusions] The first detection of CO lines has provided a new way to investigate the 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 OH1612MHz and H2O masers are located in the side walls and at the farthest ends of the bipolar lobes, respectively. Further observations are highly desired to understand the very low 12CO/13CO line ratio.