[论文解读] Absolute dimensions of eclipsing binaries. XXVI. Setting a new standard: Masses, radii, and abundances for the F-type systems AD Bootis, VZ Hydrae, and WZ Ophiuchi

J. V. Clausen, Guillermo Torres+6 more|ArXiv.org|Jun 19, 2008

Stellar, planetary, and galactic studies参考文献 66被引用 33

一句话总结

本研究利用多历元测光、径向速度数据和高分辨率光谱，对三颗F型食双星（AD Bootis、VZ Hydrae 和 WZ Ophiuchi）进行了高精度的质量、半径和元素丰度测量。该研究为检验恒星演化模型设立了新基准，揭示了WZ Ophiuchi模型预测的有效温度存在偏差，可能源于星际消光被低估，或恒星本身的内在属性（如氦含量较低或对流减弱）所致。

ABSTRACT

We determine absolute dimensions and abundances for the three F-type main-sequence detached eclipsing binaries AD Boo, VZ Hya, and WZ Oph and perform a detailed comparison with results from recent stellar evolutionary models. uvby light curves and standard photometry were obtained at ESO,radial velocity observations at CfA facilities, and high-resolution spectra with ESO's FEROS spectrograph. State-of-the-art methods were applied for the analyses. Masses and radii that are precise to 0.5-0.7% and 0.4-0.9%, respectively, have been established for the components, which span the ranges of 1.1 to 1.4 M_sun and 1.1 to 1.6 R_sun. The [Fe/H] abundances are from -0.27 to +0.10, with uncertainties between 0.07 and 0.15 dex. We find indications of a slight alpha-element overabundance of [alpha/Fe] ~ +0.1$ for WZ Oph. The secondary component of AD Boo and both components of WZ Oph appear to be slightly active. Yale-Yonsai and Victoria-Regina evolutionary models fit the components of AD Boo and VZ Hya almost equally well, assuming coeval formation, at ages of about 1.75/1.50 Gyr (AD Boo) and 1.25/1.00 Gyr (VZ Hya). BaSTI models, however, predict somewhat different ages for the primary and secondary components. For WZ Oph, the models from all three grids are significantly hotter than observed. A low He content, decreased envelope convection coupled with surface activity, and/or higher interstellar absorption would remove the discrepancy, but its cause has not been definitively identified. We have demonstrated the power of testing and comparing recent stellar evolutionary models using eclipsing binaries, provided their abundances are known. The strongest limitations and challenges are set by T_eff and interstellar absorption determinations, and by their effects on and correlation with abundance results.

研究动机与目标

• 以前所未有的精度测定三颗F型主序分光双星的绝对参数和化学丰度。
• 利用这些系统的实测数据检验现代恒星演化模型（Yale-Yonsei、Victoria-Regina、BaSTI）的性能。
• 研究WZ Ophiuchi中观测与模型预测有效温度之间的显著差异。
• 评估星际消光、氦丰度和表面活动对模型拟合一致性的影响。
• 为高精度双星研究在检验恒星演化理论方面建立新基准。

提出的方法

• 使用欧洲南方天文台拉西拉天文台的斯特罗姆伦自动望远镜获取UVBY光曲线和uvbyβ标准测光数据。
• 通过哈佛-史密松森天体物理中心和欧洲南方天文台FEROS光谱仪获取的高分辨率光谱测量径向速度。
• 采用EBOP和Wilson-Devinney双星光曲线建模程序推导轨道和物理参数。
• 应用二维互相关和光谱分解技术，以获得各组分的径向速度和光谱。
• 使用VWA丰度分析工具，从高分辨率光谱中确定铁和α-元素的丰度。
• 利用JHKs测光估算星际消光，并通过Knude的校准方法进行标定。

实验结果

研究问题

• RQ1 利用多波段测光和径向速度数据，F型主序食双星的质量和半径能以多高的精度确定？
• RQ2 当前的恒星演化模型（Yale-Yonsei、Victoria-Regina、BaSTI）在多大程度上能再现这些系统的观测质量、半径和有效温度？
• RQ3 WZ Ophiuchi中观测与模型预测有效温度之间显著差异的原因是什么？
• RQ4 表面活动、氦丰度和星际消光如何影响观测参数与理论模型的一致性？
• RQ5 元素丰度测量（Fe/H 和 α/Fe）能否有助于解决F型双星系统中模型与数据之间的不一致？

主要发现

• 对于质量在1.1至1.4 M☉之间、半径在1.1至1.6 R☉之间的恒星，质量和半径的精度分别达到0.5–0.7%和0.4–0.9%。
• 铁丰度[Fe/H]范围为−0.27至+0.10，不确定度为0.07–0.15 dex，WZ Ophiuchi中发现可能存在[α/Fe] ≈ +0.1的α-元素过量丰度。
• AD Bootis的次星以及WZ Ophiuchi的两个组分均表现出轻微表面活动的迹象，可能影响温度测定。
• Yale-Yonsei和Victoria-Regina模型在假设双星共生成的年龄约为1.75/1.50 Gyr（AD Bootis）和1.25/1.00 Gyr（VZ Hydrae）时，能较好拟合AD Bootis和VZ Hydrae的观测数据。
• BaSTI模型对AD Bootis和VZ Hydrae组分的年龄预测存在显著差异，表明年龄估计具有模型依赖性。
• 对于WZ Ophiuchi，所有三套模型网格预测的有效温度均显著高于观测值，表明模型物理或输入参数（如星际消光或氦丰度）仍存在未解决的问题。