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- Kravchenko, Kateryna, et al.
(författare)
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Tomography of cool giant and supergiant star atmospheres : III. Validation of the method on VLTI/AMBER observations of the Mira star S Ori
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 642
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Tidskriftsartikel (refereegranskat)abstract
- Context. Asymptotic giant branch (AGB) stars are characterized by substantial mass loss, however the mechanism behind it not yet fully understood. The knowledge of the structure and dynamics of AGB-star atmospheres is crucial to better understanding the mass loss. The recently established tomographic method, which relies on the design of spectral masks containing lines that form in given ranges of optical depths in the stellar atmosphere, is an ideal technique for this purpose.Aims. We aim to validate the capability of the tomographic method in probing different geometrical depths in the stellar atmosphere and recovering the relation between optical and geometrical depth scales.Methods. We applied the tomographic method to high-resolution spectro-interferometric VLTI/AMBER observations of the Mira-type AGB star S Ori. The interferometric visibilities were extracted at wavelengths contributing to the tomographic masks and fitted to those computed from a uniform disk model. This allows us to measure the geometrical extent of the atmospheric layer probed by the corresponding mask. We then compared the observed atmospheric extension with others measured from available 1D pulsation CODEX models and 3D radiative-hydrodynamics CO5BOLD simulations.Results. While the average optical depths probed by the tomographic masks in S Ori decrease (with log tau(0) = -0.45, - 1.45, and - 2.45 from the innermost to the central and outermost layers), the angular diameters of these layers increase, from 10.59 0.09 mas through 11.84 +/- 0.17 mas, up to 14.08 +/- 0.15 mas. A similar behavior is observed when the tomographic method is applied to 1D and 3D dynamical models.Conclusions. This study derives, for the first time, a quantitative relation between optical and geometrical depth scales when applied to the Mira star S Ori, or to 1D and 3D dynamical models. In the context of Mira-type stars, knowledge of the link between the optical and geometrical depths opens the way to deriving the shock-wave propagation velocity, which cannot be directly observed in these stars.
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| 2. |
- Prinoth, Bibiana, et al.
(författare)
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Titanium oxide and chemical inhomogeneity in the atmosphere of the exoplanet WASP-189 b
- 2022
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 6:4, s. 449-457
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Tidskriftsartikel (refereegranskat)abstract
- The temperature of an atmosphere decreases with increasing altitude, unless a shortwave absorber that causes a temperature inversion exists. Ozone plays this role in the Earth’s atmosphere. In the atmospheres of highly irradiated exoplanets, the shortwave absorbers are predicted to be titanium oxide (TiO) and vanadium oxide (VO). Detections of TiO and VO have been claimed using both low-, and high- spectral-resolution observations, but subsequent observations have failed to confirm these claims or overturned them. Here we report the unambiguous detection of TiO in the ultra-hot Jupiter WASP-189 b using high-resolution transmission spectroscopy. This detection is based on applying the cross-correlation technique to many spectral lines of TiO from 460 to 690 nm. Moreover, we report detections of metals, including neutral and singly ionized iron and titanium, as well as chromium, magnesium, vanadium and manganese (Fe, Fe+, Ti, Ti+, Cr, Mg, V, Mn). The line positions of the detected species differ, which we interpret as a consequence of spatial gradients in their chemical abundances, such that they exist in different regions or dynamical regimes. This is direct observational evidence for the three-dimensional thermochemical stratification of an exoplanet atmosphere derived from high-resolution ground-based spectroscopy.
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