The Distribution of SiO in the Circumstellar Envelope around IRC +10216

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.

NATURVETENSKAP Fysik Astronomi, astrofysik och kosmologi hsv//swe
NATURAL SCIENCES Physical Sciences Astronomy, Astrophysics and Cosmology hsv//eng
Stars: Circumstellar Matter
Stars: Abundances
Stars: AGB and Post-AGB
Stars: Carbon
Stars: Individual: Alphanumeric: IRC +10216
Stars: Mass Loss
Formation and development of stars
Stjärnors bildning och utveckling

Fong, David (författare)
Olofsson, HansStockholms universitet,Institutionen för astronomi(Swepub:su)olofs (författare)
Zhang, Qizhou (författare)
Patel, Nimesh (författare)
Stockholms universitetInstitutionen för astronomi (creator_code:org_t)

Ingår i:The Astrophysical Journal: American Astronomical Society649:2, s. 965-9720004-637X1538-4357

Av författaren/redakt...: Schöier, Fredrik; Fong, David; Olofsson, Hans; Zhang, Qizhou; Patel, Nimesh

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