Non-equilibrium chemistry and dust formation in AGB stars as probed by SiO line emission
| Autor: | Schoeier, F. L., Olofsson, H., Wong, T., Fong, D., Lindqvist, M., Sjouwerman, L. O. |
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| Rok vydání: | 2007 |
| Předmět: | |
| Druh dokumentu: | Working Paper |
| Popis: | 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. Comment: 2 pages, 1 figure. To be published in the proceedings of the conference "Why Galaxies Care about AGB Stars", held in Vienna, August 7-11, 2006; F. Kerschbaum, C. Charbonnel, B. Wing eds, ASP Conf.Ser. in press |
| Databáze: | arXiv |
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