Astronomy and Astrophysics, volume 285, 247-271 (1994/5-1)
Molecular observations of O- and C-rich circumstellar envelopes.
BUJARRABAL V., FUENTE A. and OMONT A.
Abstract (from CDS):
We present observations of 10 microwave transitions of the molecules SiO, HCN, HNC, SiS, HC3N, CS, SO, and 13CO in a total sample of 47 evolved stars. The studied sources are mainly O- and C-rich standard AGB stars, as well as O-rich red supergiants, S-type stars, protoplanetary nebulae and detached envelopes. We also take into account observations of these transitions, as well as of 12CO J=1-0, from the literature. We find that the molecules can be classified as "O-like" (SiO and SO) and "C-like" (HCN, HNC, SiS, HC3N and CS). The emission of O-like molecules is significantly stronger in O-rich stars than in C-rich sources, and the opposite holds for C-like species. The behaviour of 12CO and 13CO is found to be intermediate between those of O-/C-like species. We have estimated the molecular abundances in most of the studied objects. Our results indicate that the abundance of the carbon-bearing molecules HCN, HNC and CS in O-rich circumstellar envelopes can only be explained assuming the presence of an active photochemistry in their outer layers. In other cases, such as HCN and CS in C-rich AGB stars, the derived abundances are compatible with LTE chemical models. The SiO and SiS abundances in O-rich and C-rich standard sources can also be explained by LTE chemistry if we assume moreover some depletion onto grains. We finally discuss the chemical properties of some individual interesting sources.
stars: abundances - stars: circumstellar matter - stars: late type - stars: AGB, post-AGB - radio lines: stars
VizieR on-line data:
<Available at CDS (J/A+A/285/247): tables 3,4,5,6,7,8>
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