The Distribution of SiO in the Circumstellar Envelope around IRC +10216
2006 (English)In: The Astrophysical Journal, ISSN 0004-637X, Vol. 649, no 2, 965-972 p.Article in journal (Refereed) Published
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 multitransition single-dish observations, including infrared observations of rovibrational transitions, detailed radiative transfer modeling suggests that the fractional abundance of SiO in the inner part of the envelope, between ~3 and 8 stellar radii, is as high as ~1.5×10-6. 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 (re~2.4×1016 cm) low fractional abundance (f0~1.7×10-7) 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 2-5 on an angular scale corresponding to a timescale of about 200 yr. In addition, constraints on the velocity structure of the wind are obtained.
Place, publisher, year, edition, pages
2006. Vol. 649, no 2, 965-972 p.
Stars: Circumstellar Matter, Stars: Abundances, Stars: AGB and Post-AGB, Stars: Carbon, Stars: Individual: Alphanumeric: IRC +10216, Stars: Mass Loss
Astronomy, Astrophysics and Cosmology
IdentifiersURN: urn:nbn:se:su:diva-20158DOI: doi:10.1086/506199OAI: oai:DiVA.org:su-20158DiVA: diva2:186683