Volume 367, Number 3, March I 2001
|Page(s)||826 - 830|
|Section||Interstellar and circumstellar matter|
|Published online||15 March 2001|
Probing the post-AGB nature of HD 179821*
A new radio study of its circumstellar envelope
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
Corresponding author: E. Josselin, email@example.com
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
© ESO, 2001
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