Comparison of dynamical model atmospheres of Mira variables with mid-infrared interferometric and spectroscopic observations

Abstract

We present a comparison of dynamical model atmospheres with mid-infrared (~11 micron) 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 micron 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 micron 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 micron 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 micron 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.

9 pages, 6 figures, accepted for publication in A&A

References in corpus (13)

• Reprocessing the Hipparcos data for evolved stars III Revised Hipparcos period-luminosity relationship for galactic long-period variable stars
• Interferometric observations of the supergiant stars alpha Orionis and alpha Herculis with FLUOR at IOTA
• Interferometric observations of the Mira star o Ceti with the VLTI/VINCI instrument in the near-infrared
• Multi-wavelength Diameters of Nearby Miras and Semiregulars
• Dust Scattering in Miras R Car and RR Sco resolved by optical interferometric polarimetry
• Warm water vapor envelope in Mira variables and its effects on the apparent size from the near-infrared to the mid-infrared
• Pulsation of M-type Mira variables with moderately different mass: search for observable mass effects
• Warm water vapor envelope in the supergiants alf Ori and alf Her and its effects on the apparent size from the near-infrared to the mid-infrared
• Optical and Near-IR Spectra of O-rich Mira Variables : a Comparison between Models and Observations
• The K-band intensity profile of R Leonis probed by VLTI/VINCI
• Diameters of Mira Stars Measured Simultenously in the J,H,K' Near-Infrared Bands
• The structure of H2O shells in Mira atmospheres: Correlation with disk brightness distributions and a spectrophotometric signature
• Are dust shell models well-suited to explain interferometric data of late-type stars in the near-infrared?

Cited by in corpus (9)

• An Improved Model of SiO Maser Emission in Miras
• The Mira variable S Ori: Relationships between the photosphere, molecular layer, dust shell, and SiO maser shell at 4 epochs
• Pre-maximum spectro-imaging of the Mira star T Lep with AMBER/VLTI
• High-resolution observations of gas and dust around Mira using ALMA and SPHERE/ZIMPOL
• Dust-driven winds of AGB stars: The critical interplay of atmospheric shocks and luminosity variations
• Temporal variations of the outer atmosphere and the dust shell of the carbon-rich Mira variable V Oph probed with VLTI/MIDI
• Infrared Spectroscopy of Symbiotic Stars. XII. The Neutron Star SyXB System 4U 1700+24 = V934 Herculis
• Spatially resolving the outer atmosphere of the M giant BK Vir in the CO first overtone lines with VLTI/AMBER
• AMBER observations of the AGB star RS Cap: extended atmosphere and comparison with stellar models