EDP Sciences
Free access
Volume 367, Number 3, March I 2001
Page(s) 826 - 830
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20000496

A&A 367, 826-830 (2001)
DOI: 10.1051/0004-6361:20000496

Probing the post-AGB nature of HD 179821

A new radio study of its circumstellar envelope
E. Josselin1, 2 and A. Lèbre2

1  Observatorio Astronómico Nacional (OAN), IGN, Apartado 1143, 28800 Alcalá de Henares, Spain
2  GRAAL-CC72, UMR 5024-ISTEEM, CNRS/Univ. Montpellier II, Place E. Bataillon, 34095 Montpellier Cedex, France

(Received 25 April 2000 / Accepted 13 November 2000 )

In spite of recent detailed studies, the nature of HD 179821 is still puzzling. It is classified either as an intermediate-mass post-AGB star or as a massive supergiant. We present here new high sensitivity radio observations of HD 179821 in the circumstellar 12CO and 13CO lines. We also report the new detection of HCO+ in this object. The 12CO line intensities allow estimations of the mass-loss rate of HD 179821 and of the dynamical age of its circumstellar envelope. The comparison between 12CO and 13CO lines indicates an isotopic ratio for carbon of at most 5. Such a low value is characteristic of (post-)AGB stars with low-mass progenitors. Furthermore, the HCO+ molecular ion indicates that an active photochemistry occurs in the envelope of HD 179821, probably induced by UV photons emitted as the central post-AGB star warms up and/or by shocks generated by interacting winds.

Key words: stars: AGB and post-AGB -- stars: circumstellar matter -- stars: individual: HD 179821

Offprint request: E. Josselin, josselin@graal.univ-montp2.fr

SIMBAD Objects in preparation

© ESO 2001