标题： 食双星LL Aqr中的太阳孪生星 显示英文标题

标题： A solar twin in the eclipsing binary LL Aqr

摘要： 在研究太阳附近食双星项目的进程中，我们发现LL Aqr的冷伴星是一颗太阳孪生星候选体。这是首颗已知存在于非相互作用食双星系统中的具有太阳孪生星性质的恒星，为以极高的精度全面描述其物理特性提供了绝佳的机会。我们利用了广泛的多波段存档测光数据以及Super-WASP项目提供的高分辨率光谱，并从HARPS和CORALIE光谱仪获得了高分辨率光谱。两颗分量的光谱被分解，并进行了详细的LTE丰度分析。光变曲线和视向速度曲线同时使用Wilson-Devinney代码进行了分析。由此得到的极高精度的恒星参数被用于与PARSEC、MESA和GARSTEC恒星演化模型进行详细对比。 天鹰座LL由两颗主序星（F9 V + G3 V）组成，质量分别为M1 = 1.1949$\pm$0.0007 和 M2 = 1.0337$\pm$0.0007 $M_\odot$，半径分别为R1 = 1.321$\pm$0.006 和 R2 = 1.002$\pm$0.005 $R_\odot$，温度分别为T1=6080$\pm$45 K 和 T2=5703$\pm$50 K，具有太阳化学成分 [M/H]=0.02$\pm$0.05 dex。 次星的绝对尺寸、辐射和光度特性以及大气丰度与太阳孪生星的所有特征完全一致。两颗恒星比标准恒星演化模型预测的温度低约3.5$\sigma$，金属丰度低5$\sigma$。当进行高级建模时，我们发现只有那些难以接受的混合长度和包层过度对流参数值才能完全符合观测结果。使用MESA和GARSTEC代码找到的最合理且有物理依据的模型拟合仍然与观测结果存在差异，但仅在1$\sigma$的水平上。 显示英文摘要

摘要： In the course of a project to study eclipsing binary stars in vinicity of the Sun, we found that the cooler component of LL Aqr is a solar twin candidate. This is the first known star with properties of a solar twin existing in a non-interacting eclipsing binary, offering an excellent opportunity to fully characterise its physical properties with very high precision. We used extensive multi-band, archival photometry and the Super-WASP project and high-resolution spectroscopy obtained from the HARPS and CORALIE spectrographs. The spectra of both components were decomposed and a detailed LTE abundance analysis was performed. The light and radial velocity curves were simultanously analysed with the Wilson-Devinney code. The resulting highly precise stellar parameters were used for a detailed comparison with PARSEC, MESA, and GARSTEC stellar evolution models. LL Aqr consists of two main-sequence stars (F9 V + G3 V) with masses of M1 = 1.1949$\pm$0.0007 and M2=1.0337$\pm$0.0007 $M_\odot$, radii R1 = 1.321$\pm$0.006 and R2 = 1.002$\pm$0.005 $R_\odot$, temperatures T1=6080$\pm$45 K and T2=5703$\pm$50 K and solar chemical composition [M/H]=0.02$\pm$0.05 dex. The absolute dimensions, radiative and photometric properties, and atmospheric abundances of the secondary are all fully consistent with being a solar twin. Both stars are cooler by about 3.5 $\sigma$ or less metal abundant by 5$\sigma$ than predicted by standard sets of stellar evolution models. When advanced modelling was performed, we found that full agreement with observations can only be obtained for values of the mixing length and envelope overshooting parameters that are hard to accept. The most reasonable and physically justified model fits found with MESA and GARSTEC codes still have discrepancies with observations but only at the level of 1$\sigma$.