Volume 542, June 2012
|Number of page(s)||12|
|Section||Interstellar and circumstellar matter|
|Published online||25 May 2012|
CO observations of water-maser post-asymptotic giant branch stars and detection of a high-velocity outflow in IRAS 15452–5459
Centro de Astrobiología, INTA-CSIC, ctra de Ajalvir km 4,
Torrejón de Ardoz,
2 Max-Planck-Institut für Radioastronomie (MPIfR), Auf dem Hügel 69, 53121 Bonn, Germany
Received: 19 December 2011
Accepted: 21 March 2012
Many aspects of the evolutionary phase in which asymptotic giant branch stars (AGB stars) are in transition to become planetary nebulae (PNe) remain 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 timescale of this evolutionary phase, objects are rare, but their identification provides valuable probes for testing evolutionary models. We 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 assumed 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 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 1.2 × 10-4 M⊙ yr-1 (assuming optically thin emission) and 4.9 × 10-4 M⊙ 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 L⊙ and a dust mass of ~0.01 M⊙. Through the flux in the [CII] line (158 μm), we calculate a total mass of about 12 M⊙ for the circumstellar envelope, but the line is likely affected by interstellar contamination.
Key words: stars: AGB and post-AGB / circumstellar matter / submillimeter: stars
© ESO, 2012
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.