Multi-epoch VLTI/MIDI Observations of the Carbon-rich Mira Star V Oph
Ohnaka K., Driebe, T., Weigelt, G., and Wittkowski, M.
Proceedings paper for the ESO workshop "The VLT in the ELT era"
Held in Garching from October 8-12, 2007.
Springer Astrophysics and Space Science Proceedings
"Science with the VLT in the ELT Era", pg.119-123 (2009)
Abstract
The driving mechanism of mass outflows in Mira variables has not yet been fully understood. Recent progress in optical and infrared interferometric techniques has been contributing to studies of the region between the
top of the photosphere and the innermost region of the circumstellar dust shell, exactly where mass outflows are expected to be initiated. Infrared interferometric observations of oxygen-rich Mira stars have spatially
resolved dense, warm (~1000-2000 K) molecular layers consisting of H2O, SiO, and CO and extending to
~2-3 R« (e.g., Mennesson et al. 1; Perrin et al. 6; Ohnaka et al. 4). The optically thick emission from the warm
molecular layers affect the apparent size of Mira stars: the object appears larger than the star itself at wavelengths where the opacities of the above molecular species are higher. In particular, H2O has strong spectral
features in the mid-infrared, which causes the angular size to increase from the near-infrared to the mid-infrared as observed toward oxygen-rich Miras.
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