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arXiv · 1107.0842

Inhomogeneities in molecular layers of Mira atmospheres

M. Wittkowski·D. A. Boboltz·M. Ireland·I. Karovicova·K. Ohnaka·M. Scholz·F. van Wyk·P. Whitelock·P. R. Wood·A. A. Zijlstra
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Abstract

We obtained K-band spectro-interferometric observations of the Miras R Cnc, X Hya, W Vel, and RW Vel with a spectral resolution of 1500 using the VLTI/AMBER instrument. We obtained concurrent JHKL photometry using the the Mk II instrument at the SAAO. Our sources have wavelength-dependent visibility values that are consistent with earlier low-resolution AMBER observations of S Ori and with the predictions of dynamic model atmosphere series based on self-excited pulsation models. The wavelength-dependent UD diameters show a minimum near the near-continuum bandpass at 2.25 um. They increase by up to 30% toward the H2O band at 2.0 um and by up to 70% at the CO bandheads. The dynamic model atmosphere series show a consistent wavelength-dependence, and their parameters such as the visual phase, effective temperature, and distances are consistent with independent estimates. The closure phases have significantly wavelength-dependent non-zero values indicating deviations from point symmetry. For example, the R Cnc closure phase is 110 degr in the 2.0 um H2O band, corresponding for instance to an additional unresolved spot contributing 3% of the total flux at a separation of ~4 mas. Our observations are consistent with the predictions of the latest dynamic model atmosphere series based on self-excited pulsation models. The wavelength-dependent radius variations are interpreted as the effect of molecular layers. The wavelength-dependent closure phase values are indicative of deviations from point symmetry at all wavelengths, thus a complex non-spherical stratification of the extended atmosphere. In particular, the significant deviation from point symmetry in the H2O band is interpreted as a signature on large scales of inhomogeneities or clumps in the water vapor layer. The observed inhomogeneities might be caused by pulsation- and shock-induced chaotic motion in the extended atmosphere.

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M. Wittkowski, D. A. Boboltz, M. Ireland, I. Karovicova, K. Ohnaka, M. Scholz, F. van Wyk, P. Whitelock, P. R. Wood, A. A. Zijlstra. 2011-07-05. Inhomogeneities in molecular layers of Mira atmospheres. https://doi.org/10.1051/0004-6361/201117411

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