The distribution of SiO in the circumstellar envelope around IRC+10216

Abstract

New interferometric observations of SiO J=5-4 circumstellar line emission around the carbon star IRC+10216, using the Submillimeter Array, are presented. Complemented by multi-transition single-dish observations, including infrared observations of ro-vibrational transitions, detailed radiative transfer modelling suggests that the fractional abundance of SiO in the inner part of the envelope, between approximately 3-8 stellar radii, is as high as 1.5E-6. This is more than an order of magnitude higher than predicted by equilibrium stellar atmosphere chemistry in a carbon-rich environment and indicative of the importance of non-LTE chemical processes. In addition to the compact component, a spatially more extended (2.4E16 cm) low-fractional-abundance (1.7E-7) region is required to fit the observations. This suggests that the majority of the SiO molecules are effectively accreted onto dust grains in the inner wind while the remaining gas-phase molecules are eventually photodissociated at larger distances. Evidence of departure from a smooth wind is found in the observed visibilities, indicative of density variations of a factor 2 to 5 on an angular scale corresponding to a time scale of about 200 years. Additionally, constraints on the velocity structure of the wind are obtained.

Accepted for publication in ApJ, 9 pages, 9 figures

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Cited by in corpus (27)

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• The abundance of HCN in circumstellar envelopes of AGB stars of different chemical types
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• An Interferometric Spectral-line Survey of IRC+10216 in the 345 GHz Band
• Circumstellar molecular composition of the oxygen-rich AGB star IK~Tau: II. In-depth non-LTE chemical abundance analysis
• Si-bearing molecules towards IRC+10216: ALMA unveils the molecular envelope of CWLeo
• Imaging the circumstellar dust around AGB stars with PolCor
• Water in IRC+10216: a genuine formation process by shock-induced chemistry in the inner wind
• Silicon in the dust formation zone of IRC +10216 as observed with PACS and SPIRE on board Herschel
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• The complex dust formation zone of the AGB star IRC+10216 probed with CARMA 0.25 arcsec angular resolution molecular observations
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• Late Stages of Stellar Evolution - Herschel's contributions
• Herschel/HIFI observations of IRC+10216: water vapor in the inner envelope of a carbon-rich AGB star
• Chemical modelling of dust-gas chemistry within AGB outflows -- II. Effect of the dust-grain size distribution
• The chemistry of extragalactic carbon stars
• Near-infrared polarimetric study of the bipolar nebula IRAS 19312+1950
• A Review of AGB Mass Loss Imaging Techniques
• The distribution of H13CN in the circumstellar envelope around IRC+10216
• Interferometric observations of SiO thermal emission in the inner wind of M-type AGB stars IK Tauri and IRC+10011
• Multi-line study of the radial extent of SiO, CS, and SiS in AGB envelopes
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• IRC+10216 mass loss properties through the study of $\lambda$3mm emission: Large spatial scale distribution of SiO, SiS, and CS