Molecular line observations of southern S stars

J. H. Bieging, L. B.G. Knee, W. B. Latter, H. Olofsson

Research output: Contribution to journalArticlepeer-review

14 Scopus citations


We observed a sample of southern S stars with the SEST telescope, in the SiO (v=0, J=3-2) transition at 130.3 GHz, and the HCN (J=1-0) transition at 88.6 GHz. SiO emission was detected in all seven stars observed, while HCN was detected in two. We employed a statistical equilibrium/radiative transfer model to estimate the SiO abundance for an assumed molecular distribution. The inferred SiO abundances are consistent with formation of the molecule under thermodynamic equilibrium (TE) conditions near the stellar photosphere, for reasonable physical conditions. We also model the HCN emission by a similar analysis, and find that if HCN is produced near the stellar photosphere, our model abundances are much higher than predicted by TE chemistry, unless the gas temperature is <1300 K and the gas density n(H2) ∼ 1012 cm-3. Under such conditions, condensation of silicate grains may enhance production of HCN for C/O ≈ 1. Alternatively, HCN may be formed by photochemical reactions in the outer circumstellar envelope, as has been proposed for O-rich giants.

Original languageEnglish (US)
Pages (from-to)811-821
Number of pages11
JournalAstronomy and astrophysics
Issue number3
StatePublished - Nov 20 1998


  • Circumstellar matter
  • Stars: AGB
  • Stars: chemically peculiar
  • Stars: mass-loss

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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