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arXiv 0911.4422astro-ph.SRastro-ph.IM
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VX Sgr非均匀外层大气的VLTI/AMBER光谱干涉成像

VLTI/AMBER spectro-interferometric imaging of VX Sgr's inhomogenous outer atmosphere

A. Chiavassa, S. Lacour, F. Millour, T. Driebe, M. Wittkowski, B. Plez, E. Thiebeaut, E. Josselin, B. Freytag, M. Scholz, X. Haubois

摘要:

目标。我们的目标是探索光球的非常冷的晚型恒星VX Sgr,特别是分子层以上的连续形成光球的存在和表征。方法.我们用VLTI/AMBER干涉仪在光谱域1.45- 1.50中用条纹跟踪仪FINITO获得了干涉观测结果。我们对不同波长段的干涉数据进行了独立的图像重建,并用几何玩具模型拟合了干涉数据,并将数据与Miras的一维动力学模型进行了比较大气和红超巨星(RSG)和渐近巨星分支(AGB)恒星的三维流体动力学模拟。结果重建的图像和可见光显示出很强的波长依赖性。H波段图像显示两个亮点,其位置由几何玩具模型确认。的不均匀性定性预测的三维模拟。在大约2,00微米和2,35 - 2,50微米的区域中,光球出现扩展,半径大于H带。在这个光谱区域中,几何玩具模型将第三个亮点定位在光球层之外,这可能是分子层的特征。可见度的波长依赖性可以用Mira大气的一维动力学模型定性地解释。最佳拟合的光球模型显示出与观测到的vibrium很好的匹配,给出的光球直径为θ = 8.82 ± 0.50 mas。H2O分子似乎是分子层中的主要吸收剂。结论.我们表明,VX Sgr的大气,而不是RSG模型大气的Mira/AGB星模型大气。特别是,我们看到了Mira星典型的分子(水)层。

英文摘要:

Aims. We aim to explore the photosphere of the very cool late-type star VX Sgr and in particular the existence and characterization of molecular layers above the continuum forming photosphere. Methods. We obtained interferometric observations with the VLTI/AMBER interferometer using the fringe tracker FINITO in the spectral domain 1.45-2.50 micron with a spectral resolution of about 35 and baselines ranging from 15 to 88 meters.We perform independent image reconstruction for different wavelength bins and fit the interferometric data with a geometrical toy model.We also compare the data to 1D dynamical models of Miras atmosphere and to 3D hydrodynamical simulations of red supergiant (RSG) and asymptotic giant branch (AGB) stars. Results. Reconstructed images and visibilities show a strong wavelength dependence. The H-band images display two bright spots whose positions are confirmed by the geometrical toy model. The inhomogeneities are qualitatively predicted by 3D simulations. At about 2,00 micron and in the region 2,35 - 2,50 micron, the photosphere appears extended and the radius is larger than in the H band. In this spectral region, the geometrical toy model locates a third bright spot outside the photosphere that can be a feature of the molecular layers. The wavelength dependence of the visibility can be qualitatively explained by 1D dynamical models of Mira atmospheres. The best-fitting photospheric models show a good match with the observed visibilities and give a photospheric diameter of theta = 8,82+-0,50 mas. The H2O molecule seems to be the dominant absorber in the molecular layers. Conclusions. We show that the atmosphere of VX Sgr rather resembles Mira/AGB star model atmospheres than RSG model atmospheres. In particular, we see molecular (water) layers that are typical for Mira stars.

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