Publications of the MPIfR Optical & Infrared Interferometry Group
Ohnaka, K., Scholz, M., Wood, P.R.:
Comparison of dynamical model atmospheres of
Mira variables with
mid-infrared interferometric and spectroscopic observations
Astronomy & Astrophysics, 446
No.3, pg.1119-1127 (2006)
m) interferometric
and spectroscopic observations of the Mira variable o Cet.
The dynamical model atmospheres of Mira variables pulsating in the
fundamental mode can fairly explain, without assuming ad-hoc
components, the seemingly contradictory mid-infrared spectroscopic and
interferometric observations of o Cet: the 11 m sizes measured in
the bandpass without any salient spectral features are about twice as
large as those measured in the near-infrared. Our calculations of
synthetic spectra show that the strong absorption due to a number of
optically thick H2O lines is filled in by the emission of
these H2O lines originating in the geometrically extended
layers, providing a possible physical explanation for the picture
proposed by Ohnaka (2004a) based on a semi-empirical modeling. This
filling-in effect results in rather featureless, continuum-like spectra
in rough agreement with the observed high-resolution 11 m spectra, although
the models still predict the H2O lines to be more pronounced
than the observations. The inverse P-Cyg profiles of some strong H2O
lines observed in the 11 m spectra can also be
reasonably reproduced by our dynamical model atmospheres. The presence
of the extended H2O layers manifests itself as mid-infrared
angular diameters much larger than the continuum diameter. The 11 m uniform-disk
diameters predicted by our dynamical model atmospheres are in fair
agreement with those observed with the Infrared Spatial Interferometer
(ISI), but still somewhat smaller than the observed diameters. We
discuss possible reasons for this discrepancy and problems with the
current dynamical model atmospheres of Mira variables.
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