利用 Gaia 视差测量与 CO5BOLD RHD 模拟反演 AGB 星恒星参数与动力学
Retrieving stellar parameters and dynamics of AGB stars with Gaia parallax measurements and CO5BOLD RHD simulations
AI总结：
本文利用 CO5BOLD 三维 RHD 模拟与 Gaia 视差观测，建立光心位移与恒星参数的解析关系，从而从视差不确度中反演 AGB 星的表面重力、有效温度和半径。
摘要：
背景。渐近巨星支（AGB）星的复杂动力学及其产生的星风对恒星参数测量有显著影响，并放大了这些参数的不确定性。对流的三维（3D）辐射流体动力学（RHD）模拟表明，AGB 星表面的对流相关结构会影响 Gaia 测得的光心位移和视差不确度。目的。我们探索对流对光心变化的影响，并旨在建立光心位移与恒星参数之间的解析关系，从而从视差不确度中反演这些参数。方法。我们选取了 31 个使用 CO5BOLD 的 RHD 模拟，并利用后处理辐射转移程序 Optim3D 计算 Gaia G 波段 [320-1050 nm] 的强度图。基于这些强度图，我们计算了光心位置及其时间涨落。随后，我们将合成的标准差与 Gaia 观测到的 53 颗 Mira 变星样本的视差不确度进行了比较。结果。模拟显示光心在恒星表面的位移范围为相应恒星半径的 4% 至 13%，与先前研究一致。我们给出了联系模拟脉动周期与光心位移以及脉动周期与恒星参数的解析关系。通过结合这些关系，我们反演得到了样本中恒星的表面重力、有效温度和半径。结论。我们的分析突出了一种原创方法，即同时利用最先进的 AGB 星对流三维数值模拟和 AGB 星的视差观测来反演恒星参数。这将有助于我们加深对这些巨星的理解。
英文摘要：
Context. The complex dynamics of asymptotic giant branch (AGB) stars and the resulting stellar winds have a significant impact on the measurements of stellar parameters and amplify their uncertainties. Three-dimensional (3D) radiative hydrodynamic (RHD) simulations of convection suggest that convection-related structures at the surface of AGB star affect the photocentre displacement and the parallax uncertainty measured by Gaia. Aims. We explore the impact of the convection on the photocentre variability and aim to establish analytical laws between the photocentre displacement and stellar parameters to retrieve such parameters from the parallax uncertainty. Methods. We used a selection of 31 RHD simulations with CO5BOLD and the post-processing radiative transfer code Optim3D to compute intensity maps in the Gaia G band [320-1050 nm]. From these maps, we calculated the photocentre position and temporal fluctuations. We then compared the synthetic standard deviation to the parallax uncertainty of a sample of 53 Mira stars observed with Gaia. Results. The simulations show a displacement of the photocentre across the surface ranging from 4 to 13 % of the corresponding stellar radius, in agreement with previous studies. We provide an analytical law relating the pulsation period of the simulations and the photocentre displacement as well as the pulsation period and stellar parameters. By combining these laws, we retrieve the surface gravity, the effective temperature, and the radius for the stars in our sample. Conclusions. Our analysis highlights an original procedure to retrieve stellar parameters by using both state-of-the-art 3D numerical simulations of AGB stellar convection and parallax observations of AGB stars. This will help us refine our understanding of these giants.
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