Non-equilibrium chemistry and dust formation in AGB stars as probed by SiO line emission

Details Non-equilibrium chemistry and dust formation in AGB stars as probed by SiO line emission Non-equilibrium chemistry and dust formation in AGB stars as probed by SiO line emission

2007-05-18

arxiv.org/abs/0705.2651v1

Astronomy and Astrophysics

Astrophysics

2 pages, 1 figure. To be published in the proceedings of the conference "Why Galaxies Care about AGB Stars", held in Vienna, A

Scientific paper

We have performed high spatial resolution observations of SiO line emission for a sample of 11 AGB stars using the ATCA, VLA and SMA interferometers. Detailed radiative transfer modelling suggests that there are steep chemical gradients of SiO in their circumstellar envelopes. The emerging picture is one where the radial SiO abundance distribution starts at an initial high abundance, in the case of M-stars consistent with LTE chemistry, that drastically decreases at a radius of ~1E15 cm. This is consistent with a scenario where SiO freezes out onto dust grains. The region of the wind with low abundance is much more extended, typically ~1E16 cm, and limited by photodissociation. The surpisingly high SiO abundances found in carbon stars requires non-equilibrium chemical processes.

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