[论文解读] The nearby eclipsing stellar system delta Velorum. II. First reliable orbit for the eclipsing pair

T. Pribulla, A. Mérand+9 more|HAL (Le Centre pour la Communication Scientifique Directe)|Dec 29, 2010

Stellar, planetary, and galactic studies被引用 11

一句话总结

本研究利用高分辨率光谱和光变曲线，首次获得了附近多星系统δ Velorum中食双星成分的可靠光谱轨道。该研究精确测定了质量（2.53±0.11 M⊙ 和 2.37±0.10 M⊙）、半径和轨道参数，揭示了恒星快速自转且已离开主序，系统年龄约为~400 Myr。

ABSTRACT

Context. The nearby multiple system delta Velorum contains a widely detached eclipsing binary and a third component. Aims. We take advantage of this system offering the opportunity to determine the set of fundamental parameters (masses, luminosities, and radii) of three coeval stars with sufficient precision to test models of stellar evolution. Methods. Extensive high-resolution spectroscopy is analyzed by the broadening function technique to provide the first spectroscopic orbit of the eclipsing pair. Simultaneous analysis of the spectroscopic data and the SMEI satellite light curve is performed to provide astrophysical parameters for the components. We use a modified Roche model assuming an eccentric orbit and asynchronous rotation. Results. The observations show that components of the eclipsing pair rotate at about two-thirds of the break-up velocity, which excludes any chemical peculiarity and results in a non-uniform surface brightness. Although the inner orbit is eccentric, no apsidal motion is seen during the SMEI photometric observations. For the inner orbit, the orbital parameters are eccentricity e = 0.29, longitude of the periastron passage omega = 109 degrees, and inclination 89.0 degrees. Conclusions. Component's masses MAa = 2.53+/-0.11 Msun, MAb = 2.37+/-0.10 Msun and MB = 1.5 Msun combined with inferred radii of Aa and Ab components indicate that the eclipsing pair has already left the Main sequence and the estimated age of the system is about 400 Myr.

研究动机与目标

• 以高精度测定δ Velorum食双星成分的基本天体物理参数。
• 解决由于先前光谱和测光数据有限且不一致，导致系统轨道和物理参数长期存在的模糊性。
• 通过获取附近系统中三颗共演化恒星的精确质量、半径和有效温度，检验恒星演化模型。
• 研究快速自转对恒星表面亮度和温度分布的影响。
• 利用时间和测光数据改进宽距目视双星AB的轨道解。

提出的方法

• 利用分辨率较高的阶梯光谱仪获取并分析光谱，采用轮廓展宽函数技术提取视向速度，并解析重叠的谱线轮廓。
• 同时建模光谱数据与SMEI卫星的测光光变曲线，以约束轨道元素和恒星参数。
• 应用改进的Roche模型，考虑偏心轨道和非同步自转，描述变形且快速自转的恒星成分。
• 应用von Zeipel定理，预测由自转调制引起的非均匀表面温度分布。
• 采用傅里叶反卷积技术分离单个成分的光谱，以提高参数测定精度。
• 对比多历元测光和光谱数据，评估Rossiter-McLaughlin效应和轨道倾角。

Figure 1: Detrended and filtered (removing obvious outliers) SMEI LC of $\delta$ Vel. The data were phased using the following ephemeris for the periastron passage: To = HJD 2 452 528.950 + 45.15023 $\times E$ (see Table 2 ). Only data from 2003-2006 are plotted.

实验结果

研究问题

• RQ1 δ Velorum食双星成分的精确轨道元素是什么，包括偏心率、近日点角和倾角？
• RQ2 成分的质量和半径在多大程度上约束了系统的演化状态和年龄？
• RQ3 快速自转在多大程度上影响了恒星的表面亮度和温度分布？
• RQ4 能否使用考虑偏心轨道和非同步自转的改进Roche几何模型，一致地拟合观测到的光变曲线和光谱数据？
• RQ5 第三颗成分（B）对观测谱线的贡献是什么，如何将其分离以实现准确的参数测定？

主要发现

• 食双星的轨道偏心率为 e = 0.290，近日点角为 ω = 109°，倾角 i = 89.0°，表明轨道为近似边缘朝向。
• 成分质量测定为 M_Aa = 2.53 ± 0.11 M⊙ 和 M_Ab = 2.37 ± 0.10 M⊙，第三颗成分B的质量约为1.5 M⊙。
• 主星和次星分别以56%和62%的破裂速度自转，导致显著形变和非均匀表面亮度。
• 由于自转调制和von Zeipel效应，有效温度范围预测为Aa：9220–9780 K，Ab：9280–9880 K。
• 尽管轨道为偏心，但在SMEI测光监测期间未检测到近日点运动。
• 系统的估计年龄约为~400 Myr，与成分已离开主序的状态一致，其质量与半径也支持此结论。

Figure 2: Broadening functions close to the principal phases (counted from the primary eclipse, with the secondary occurring at phase 0.436): 0.142 (maximum separation of the components), 0.441 (end of the secondary eclipse), 0.800 (maximum separation of the components), and 0.997 (beginning of the