Interstellar SiO as a tracer of high-temperature chemistry.

Lucy M Ziurys, P. Friberg, W. M. Irvine

Research output: Contribution to journalArticle

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Abstract

The J = 2-1 transition of SiO has been searched for toward both hot and cold molecular gas. SiO was not detected toward the dark clouds TMC-1, L134 N, and B335, down to column density upper limits of N < 2-4 x 10(10) cm-2. The species, however, has been observed toward all sources with a kinetic temperature greater than or equal to 30 K, with the largest column densities (N approximately 10(13)-10(17) cm-2) measured in the warmest (TK > or = 100 K) material. The abundance of SiO, relative to HCN, is found to be approximately 0.1-1 in the massive star-forming regions toward Orion and NGC 7538; toward the dark clouds, the upper limits to this ratio is less than 0.0002-0.004. A similar enhancement in the warmer regions is reflected in the SiO/H2 ratio as well. A linear relation was found between the natural log of the SiO concentration and 1/TK, suggesting that the species' formation involves a chemically specific process that contains an activation barrier of approximately 90 K. SiO was also found to be underabundant with respect to SO in cold clouds, with SiO/SO < 1/1000, versus SiO/SO > or =, measured in Orion-KL. The formation of SiO is therefore linked closely to the local gas kinetic temperature, rather than the oxygen abundance, and its synthesis is likely to involve high-temperature gas-phase reactions. The species thus may serve as an unambiguous indicator of high-temperature or "shock" chemistry.

Original languageEnglish (US)
Pages (from-to)201-207
Number of pages7
JournalAstrophysical Journal
Volume343
Issue number1
StatePublished - Aug 1 1989
Externally publishedYes

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tracers
tracer
chemistry
gas phase reaction
cold gas
high temperature gases
molecular gases
massive stars
gas
shock
activation
vapor phases
kinetics
oxygen
augmentation
synthesis
gases
temperature
cold
indicator

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Interstellar SiO as a tracer of high-temperature chemistry. / Ziurys, Lucy M; Friberg, P.; Irvine, W. M.

In: Astrophysical Journal, Vol. 343, No. 1, 01.08.1989, p. 201-207.

Research output: Contribution to journalArticle

Ziurys, LM, Friberg, P & Irvine, WM 1989, 'Interstellar SiO as a tracer of high-temperature chemistry.', Astrophysical Journal, vol. 343, no. 1, pp. 201-207.
Ziurys, Lucy M ; Friberg, P. ; Irvine, W. M. / Interstellar SiO as a tracer of high-temperature chemistry. In: Astrophysical Journal. 1989 ; Vol. 343, No. 1. pp. 201-207.
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