Optical interferometry and Gaia measurement uncertainties reveal the physics of asymptotic giant branch stars
Optical interferometry and Gaia measurement uncertainties reveal the physics of asymptotic giant branch stars
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DOI：
10.1051/0004-6361/202037832
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发表时间：
2020-06
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影响因子：
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通讯作者：
A. Chiavassa;K. Kravchenko;F. Millour;G. Schaefer;M. Schultheis;B. Freytag;O. Creevey;V. Hocd'e
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文献类型：
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作者：
A. Chiavassa;K. Kravchenko;F. Millour;G. Schaefer;M. Schultheis;B. Freytag;O. Creevey;V. Hocd'e
上下文渐近巨星分支恒星是冷的发光的演化恒星，在整个银河系和盖亚数据中都可以很好地观察到。它们有复杂的恒星表面动力学目标。在AGB星星CL Lac上，研究表明，与对流相关的变化性是盖亚DR 2视差的很大一部分。我们观察这颗星星与MIRC-X光束组合器安装在CHARA干涉仪，以检测恒星表面的不均匀性的存在。方法.我们从不同波长的干涉观测中重建了孔径合成图像。然后，我们使用3D辐射流体动力学模拟恒星对流与CO 5 BOLD和后处理辐射传输代码Optim 3D计算强度图的MIRC-X观测的光谱通道。然后，我们确定了恒星半径，并将3D合成地图与重建的地图进行了比较，重点是在1.52和1.70微米两个不同的光谱通道上同时匹配强度对比度，恒星表面结构的形态和感光中心位置。结果我们在两个波长下测量了CL Lac的表观直径，并使用盖亚视差恢复了半径。除此之外，重建图像的特征在于存在更亮的区域，这在很大程度上影响了感光中心的位置。与3D模拟的比较表明，无论是在对比度和表面结构形态的观察，这意味着我们的模型是足够的解释所观察到的不均匀性。结论.这项工作证实了存在对流相关的表面结构的AGB星星的盖亚DR 2。我们的研究结果将有助于我们在利用盖亚测量不确定性方面向前迈出一步，使用适当的RHD模拟来提取AGB恒星的基本属性。
Context. Asymptotic giant branch stars are cool luminous evolved stars that are well observable across the Galaxy and populating Gaia data. They have complex stellar surface dynamics Aims. On the AGB star CL Lac, it has been shown that the convection-related variability accounts for a substantial part of the Gaia DR2 parallax error. We observed this star with the MIRC-X beam combiner installed at the CHARA interferometer to detect the presence of stellar surface inhomogeneities. Methods. We performed the reconstruction of aperture synthesis images from the interferometric observations at different wavelengths. Then, we used 3D radiative hydrodynamics simulations of stellar convection with CO5BOLD and the post-processing radiative transfer code Optim3D to compute intensity maps in the spectral channels of MIRC-X observations. Then, we determined the stellar radius and compared the 3D synthetic maps to the reconstructed ones focusing on matching the intensity contrast, the morphology of stellar surface structures, and the photocentre position at two different spectral channels, 1.52 and 1.70 micron, simultaneously. Results. We measured the apparent diameter of CL Lac at two wavelengths and recovered the radius using a Gaia parallax. In addition to this, the reconstructed images are characterised by the presence of a brighter area that largely affects the position of the photocentre. The comparison with 3D simulation shows good agreement with the observations both in terms of contrast and surface structure morphology, meaning that our model is adequate for explaining the observed inhomogenities. Conclusions. This work confirms the presence of convection-related surface structures on an AGB star of Gaia DR2. Our result will help us to take a step forward in exploiting Gaia measurement uncertainties to extract the fundamental properties of AGB stars using appropriate RHD simulations.