Molecular line observations of southern S stars

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

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

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
Volume339
Issue number3
StatePublished - Nov 20 1998

Fingerprint

S stars
thermodynamic equilibrium
photosphere
thermodynamics
gas density
gas temperature
gas
photochemical reactions
radiative transfer
condensation
silicates
envelopes
silicate
telescopes
chemistry
stars
estimates
molecules
temperature

Keywords

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

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Bieging, J. H., Knee, L. B. G., Latter, W. B., & Olofsson, H. (1998). Molecular line observations of southern S stars. Astronomy and Astrophysics, 339(3), 811-821.

Molecular line observations of southern S stars. / Bieging, John H; Knee, L. B G; Latter, W. B.; Olofsson, H.

In: Astronomy and Astrophysics, Vol. 339, No. 3, 20.11.1998, p. 811-821.

Research output: Contribution to journalArticle

Bieging, JH, Knee, LBG, Latter, WB & Olofsson, H 1998, 'Molecular line observations of southern S stars', Astronomy and Astrophysics, vol. 339, no. 3, pp. 811-821.
Bieging JH, Knee LBG, Latter WB, Olofsson H. Molecular line observations of southern S stars. Astronomy and Astrophysics. 1998 Nov 20;339(3):811-821.
Bieging, John H ; Knee, L. B G ; Latter, W. B. ; Olofsson, H. / Molecular line observations of southern S stars. In: Astronomy and Astrophysics. 1998 ; Vol. 339, No. 3. pp. 811-821.
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abstract = "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.",
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AU - Bieging, John H

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AU - Latter, W. B.

AU - Olofsson, H.

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N2 - 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.

AB - 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.

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KW - Stars: AGB

KW - Stars: chemically peculiar

KW - Stars: mass-loss

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