“X-Raying” a Be star disk: fundamental parameters of the eclipsing binary Be star V658 Car.

TESS and IUE data on V658 Car.

With its two stellar eclipses and two disk attenuations per binary orbit, V658 Carinae stands out as the first clear eclipsing Be + sdOB system. This rare alignment offers a unique opportunity to probe the structure and dynamics of a Be star disk with unprecedented detail. In this study, we present the most comprehensive observational dataset and modeling effort for this system to date, including optical, near-infrared, and ultraviolet spectroscopy, space-based photometry, and optical polarization. Using a new ray-tracing code, we apply a three-component model, consisting of an oblate, rapidly rotating Be star, a symmetric circumstellar disk, and a compact stripped companion, to reproduce the system’s light curve, polarization, and spectral features. Our analysis yields precise constraints on the stellar and disk parameters, determining its status as the second known late-type Be + stripped star, and also provides strong spectroscopic evidence for a tenuous circumsecondary envelope. Despite the model’s overall success, several key observables, such as the Hα equivalent width and the secondary attenuation, remain poorly reproduced, pointing to the need for more sophisticated modelling. In particular, future improvements should incorporate the companion’s radiative feedback on the disk and account for asymmetric disk structures expected by the gravitational interaction with the companion. Owing to its unique geometry and rich diagnostics, V658 Car establishes itself as a benchmark system for Be stars (and rapid rotators in general), stripped stars, post-RLOF massive binaries, and circumstellar disk structures.

凌日系外行星巡天卫星（Transiting Exoplanet Survey Satellite, TESS）与国际紫外探测器（International Ultraviolet Explorer, IUE）针对船底座V658（V658 Carinae）的观测数据。

该双星系统每个轨道周期内会出现两次恒星食与两次星盘消光事件，因此船底座V658成为首个被确凿证实的Be星+sdOB型星（subdwarf O/B）食双星系统。这种罕见的几何构型为我们以空前的细节精度研究Be星星盘的结构与动力学特性提供了独一无二的契机。
本研究中，我们发布了目前为止针对该系统最全面的观测数据集与建模研究成果，涵盖光学、近红外与紫外光谱观测、空间测光以及光学偏振测量。我们借助一款全新的光线追踪程序，采用由快速旋转的扁球形Be星、对称星周盘以及致密剥离型伴星组成的三组分模型，对该系统的光变曲线、偏振特性与光谱特征进行了拟合重现。
本次分析对恒星与星盘参数给出了精准的约束条件，确认该系统是已知第二例晚型Be星+剥离型恒星双星系统，同时还为伴星周围存在稀薄星周包层提供了强有力的光谱学证据。
尽管该模型整体拟合效果良好，但仍有若干关键观测量（如Hα等值宽度与伴星消光量）的拟合结果欠佳，这表明后续需要采用更为精细复杂的建模方案。具体而言，未来的模型优化应纳入伴星对星盘的辐射反馈效应，并考虑因与伴星的引力相互作用而预期产生的非对称星盘结构。
鉴于其独特的几何构型与丰富的诊断价值，船底座V658将成为Be星（以及广义上的快速旋转恒星）、剥离型恒星、经历洛希瓣溢出（Roche Lobe Overflow, RLOF）的大质量双星系统以及星周盘结构研究的基准参照系统。