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

References in corpus (3)

• Oxygen Chemistry in the Circumstellar Envelope of the Carbon-Rich Star IRC+10216
• The circumstellar envelope of IRC+10216 from milli-arcsecond to arcmin scales
• SiO in C-rich circumstellar envelopes of AGB stars: effects of non-LTE chemistry and grain adsorption

Cited by in corpus (14)

• A Detailed Analysis of the Dust Formation Zone of IRC+10216 Derived from Mid-IR Bands of C2H2 and HCN
• The abundance of SiS in circumstellar envelopes around AGB stars
• Si-bearing molecules towards IRC+10216: ALMA unveils the molecular envelope of CWLeo
• Water in IRC+10216: a genuine formation process by shock-induced chemistry in the inner wind
• The complex dust formation zone of the AGB star IRC+10216 probed with CARMA 0.25 arcsec angular resolution molecular observations
• Detection of `parent' molecules from the inner wind of AGB stars as tracers of non-equilibrium chemistry
• The abundance of S- and Si-bearing molecules in O-rich circumstellar envelopes of AGB stars
• Late Stages of Stellar Evolution - Herschel's contributions
• Chemical modelling of dust-gas chemistry within AGB outflows -- II. Effect of the dust-grain size distribution
• Near-infrared polarimetric study of the bipolar nebula IRAS 19312+1950
• 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
• Dense molecular clumps in the envelope of the yellow hypergiant IRC+10420