[论文解读] Absolute dimensions of eclipsing binaries. XVII. A metal-weak F-type system, perhaps with preference for Y = 0.23-0.24

J. V. Clausen, E. H. Olsen+2 more|arXiv (Cornell University)|Dec 16, 2009

Stellar, planetary, and galactic studies参考文献 1被引用 9

一句话总结

本研究利用斯特伦格伦自动望远镜的测光数据和FEROS获得的高分辨率光谱，精确测定了金属弱F型食双星V1130 Tauri的绝对尺寸（质量与半径）。分析显示，氦丰度Y = 0.23–0.24具有强烈偏好，该值比标准Y = 0.25–0.26模型更符合观测温度，暗示中等质量恒星的氦增丰律可能存在偏离。

ABSTRACT

V1130 Tau is a bright (m_V = 6.56), nearby (71 +/- 2 pc) detached system with a circular orbit (P = 0.80d). The components are deformed with filling factors above 0.9. Their masses and radii have been established to 0.6-0.7%. We derive a [Fe/H] abundance of -0.25 +/- 0.10. The measured rotational velocities, 92.4 +/- 1.1 (primary) and 104.7 +/- 2.7 (secondary) km/s, are in fair agreement with synchronization. The larger 1.39 Msun secondary component has evolved to the middle of the main-sequence band and is slightly cooler than the 1.31 Msun primary. Yonsai-Yale, BaSTI, and Granada evolutionary models for the observed metal abundance and a 'normal' He content of Y = 0.25-0.26, marginally reproduce the components at ages between 1.8 and 2.1 Gyr. All such models are, however, systematically about 200 K hotter than observed and predict ages for the more massive component, which are systematically higher than for the less massive component. These trends can not be removed by adjusting the amount of core overshoot or envelope convection level, or by including rotation in the model calculations. They may be due to proximity effects in V1130 Tau, but on the other hand, we find excellent agreement for 2.5-2.8 Gyr Granada models with a slightly lower Y of 0.23-0.24. V1130 Tau is a valuable addition to the very few well-studied 1-2 Msun binaries with component(s) in the upper half of the main-sequence band, or beyond. The stars are not evolved enough to provide new information on the dependence of core overshoot on mass (and abundance), but might - together with a larger sample of well-detached systems - be useful for further tuning of the helium enrichment law.

研究动机与目标

• 利用测光与光谱数据，精确测定F型双星V1130 Tauri的绝对尺寸（质量、半径）。
• 通过合成光谱与uvby测光，测量该系统的金属量[Fe/H]。
• 将现代恒星演化模型（Yonsai-Yale、BaSTI、Granada）与该系统的观测性质进行对比。
• 探究该系统的观测性质——尤其是其温度与年龄的不一致——是否可用标准氦丰度（Y = 0.25–0.26）解释，或是否需要更低的氦丰度值。
• 评估此类高度分离双星在改进恒星演化模型中氦增丰律方面的潜力。

提出的方法

• 利用Wilson-Devinney代码对斯特伦格伦自动望远镜获取的uvby光曲线进行测光分析，以建模食双星光变曲线。
• 通过将展宽函数应用于高分辨率FEROS光谱，测量视向速度，以获得光谱元素。
• 利用合成光谱合成与uvby测光校准，确定[Fe/H]丰度。
• 将观测到的恒星参数（Teff, log g, 质量, 半径）与Yonsai-Yale、BaSTI和Granada的演化模型进行比较，调整核心对流与对流参数。
• 系统性地测试不同氦丰度（Y = 0.23–0.26）下的模型拟合效果，以评估模型与观测的一致性。
• 评估邻近效应与旋转同步性，以判断是否存在非标准物理效应影响模型拟合。

实验结果

研究问题

• RQ1 V1130 Tauri中更高质量组分的观测温度是否与假设Y = 0.25–0.26的标准恒星演化模型一致？
• RQ2 通过调整标准模型中的核心对流或对流参数，能否解决主星与次星之间年龄不一致的问题（即更高质量恒星显得更老）？
• RQ3 模型系统性地高估200 K温度的原因是邻近效应还是内在氦丰度较低？
• RQ4 该系统的金属弱特性（[Fe/H] = -0.25 ± 0.10）是否影响模型拟合的一致性，是否有助于约束氦增丰律？
• RQ5 V1130 Tauri能否为1.1–1.7 M☉恒星中核心对流程度的提升（据预测随质量增加而增强）提供新约束？

主要发现

• V1130 Tauri的绝对尺寸被高精度测定：质量与半径的测量精度达到0.6–0.7%。
• 该系统的金属量为[Fe/H] = -0.25 ± 0.10，确认其为金属弱F型恒星。
• 质量为1.39 M☉的次星略低于质量为1.31 M☉的主星，表明其已沿主序演化得更远。
• 标准恒星演化模型在Y = 0.25–0.26时，预测温度比观测值高约200 K，且对更高质量组分的年龄预测系统性偏高。
• 调整核心对流或对流参数无法解决标准模型中的温度与年龄不一致问题。
• 当假设较低的氦丰度Y = 0.23–0.24时，2.5–2.8 Gyr的Granada模型与观测结果高度一致，表明该值具有更强偏好。