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2000ApJ...543..897B - Astrophys. J., 543, 897-921 (2000/November-2)
Submillimeter- and millimeter-wavelength observations of SiO and HCN in circumstellar envelopes of AGB stars.
BIEGING J.H., SHAKED S. and GENSHEIMER P.D.
Abstract (from CDS):
We calculated emergent spectra for model circumstellar envelopes and compare these with the observed line intensity ratios. We conclude that (1) the HCN line intensity ratios for the M stars are inconsistent with chemical models in which HCN is produced via photochemistry in the outer circumstellar envelope. HCN must be formed by a nonequilibrium chemical process in the inner envelope or extended stellar atmosphere. (2) The HCN/SiO intensity ratios of lines with similar excitation energies clearly separate the carbon stars from the M and S stars. The M and S stars show a trend of increasing HCN/SiO intensity ratios with increasing mass-loss rate. (3) These data support the idea that pulsation-driven shocks result in the formation of organic molecules like HCN in the envelopes of M stars. Observations of these molecules could give useful constraints on hydrodynamic models for stellar mass loss driven by pulsational shocks in the stellar atmosphere.
We detected emission from vibrationally excited HCN in the v=(0,11c,0), J=3-2 and 4-3 transitions toward four carbon stars. In one star, V Cyg, the lines are strong and narrow, and are most likely a result of maser amplification.
Abstract Copyright: ∼
Journal keyword(s): Masers - Molecular Processes - Radio Lines: Stars - Stars: AGB and Post-AGB - Stars: Mass Loss
Simbad objects: 29
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