CO observations of water-maser post-AGB stars and detection of a high-velocity outflow in IRAS 15452-5459

TL;DR

This study uses CO line observations to investigate the transition of AGB stars to planetary nebulae, revealing a high-velocity outflow in IRAS 15452-5459 and providing insights into envelope shaping processes.

Contribution

First detection of a high-velocity outflow in IRAS 15452-5459 using CO lines, advancing understanding of post-AGB star evolution and envelope morphology.

Findings

Detected a fast molecular outflow in IRAS 15452-5459.

Estimated mass-loss rate between 1.2x10^{-4} and 4.9x10^{-4} Msun/yr.

Derived physical properties including luminosity and dust mass for the nebula.

Abstract

Many aspects of the evolutionary phase in which Asymptotic Giant Branch stars (AGB stars) are in transition to become Planetary Nebulae (PNe) are still poorly understood. An important question is how the circumstellar envelopes of AGB stars switch from spherical symmetry to the axially symmetric structures frequently observed in PNe. In many cases there is clear evidence that the shaping of the circumstellar envelopes of PNe is linked to the formation of jets/collimated winds and their interaction with the remnant AGB envelope. Because of the short evolutionary time, objects in this phase are rare, but their identification provides valuable probes for testing evolutionary models. We have observed (sub)millimeter CO rotational transitions with the APEX telescope in a small sample of stars hosting high-velocity OH and water masers. These targets are supposed to have recently left the AGB, as indicated by the presence of winds traced by masers, with velocities larger than observed during that phase. We have carried out observations of several CO lines, ranging from J=2-1 up to J=7-6. In IRAS 15452-5459 we detect a fast molecular outflow in the central region of the nebula and estimate a mass-loss rate between 1.2x10^{-4} Msun yr^{-1} (assuming optically thin emission) and 4.9x10^{-4} Msun yr^{-1} (optically thick emission). We model the SED of this target taking advantage of our continuum measurement at 345 GHz to constrain the emission at long wavelengths. For a distance of 2.5 kpc, we estimate a luminosity of 8000 Lsun and a dust mass of 0.01 Msun. Through the flux in the [CII] line (158 um), we calculate a total mass of about 12 Msun for the circumstellar envelope, but the line is likely affected by interstellar contamination.