Inhomogeneities in molecular layers of Mira atmospheres
Aims: We investigate the structure and shape of the photospheric and molecular layers of the atmospheres of four Mira variables. Methods: We obtained near-infrared K-band spectro-interferometric observations of the Mira variables R Cnc, X Hya, W Vel, and RW Vel with a spectral resolution of about 15...
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| Main Authors: | , , , , , , , , , |
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| Format: | Article (Journal) Editorial |
| Language: | English |
| Published: |
21 July 2011
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| In: |
Astronomy and astrophysics
Year: 2011, Volume: 532, Pages: 1-5 |
| ISSN: | 1432-0746 |
| DOI: | 10.1051/0004-6361/201117411 |
| Online Access: | Verlag, lizenzpflichtig, Volltext: https://doi.org/10.1051/0004-6361/201117411 Verlag, lizenzpflichtig, Volltext: https://www.aanda.org/articles/aa/abs/2011/08/aa17411-11/aa17411-11.html 
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| Author Notes: | M. Wittkowski, D.A. Boboltz, M. Ireland, I. Karovicova, K. Ohnaka, M. Scholz, F. van Wyk, P. Whitelock, P.R. Wood, and A A. Zijlstra |
| Summary: | Aims: We investigate the structure and shape of the photospheric and molecular layers of the atmospheres of four Mira variables. Methods: We obtained near-infrared K-band spectro-interferometric observations of the Mira variables R Cnc, X Hya, W Vel, and RW Vel with a spectral resolution of about 1500 using the AMBER instrument at the VLTI. We obtained concurrent JHKL photometry using the the Mk II instrument at the SAAO. Results: The Mira stars in our sample are found to 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 corresponding wavelength-dependent uniform disk (UD) diameters show a minimum near the near-continuum bandpass at 2.25 μm. They then increase by up to 30% toward the H2O band at 2.0 μm and by up to 70% at the CO bandheads between 2.29 μm and 2.48 μm. 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 and non-zero values at all wavelengths indicating deviations from point symmetry. For example, the R Cnc closure phase is 110° ± 4° in the 2.0 μm H2O band, corresponding for instance to an additional unresolved spot contributing 3% of the total flux at a separation of ~4 mas. Conclusions: 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 lying above the photosphere. 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 (there being a few across the stellar disk) of inhomogeneities or clumps in the water vapor layer. The observed inhomogeneities might possibly be caused by pulsation- and shock-induced chaotic motion in the extended atmosphere. |
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| Item Description: | Gesehen am 21.11.2022 |
| Physical Description: | Online Resource |
| ISSN: | 1432-0746 |
| DOI: | 10.1051/0004-6361/201117411 |