While mass transfer in binary systems is a crucial aspect of binary evolution models, it remains far from understood. HD 352 is a spectroscopic binary exhibiting ellipsoidal variability, likely due to a tidally deformed giant donor filling its Roche lobe and transferring matter to a faint companion. Here, we analyze VLTI/PIONIER interferometric observations of the system, obtained between 2010 to 2020. We demonstrate that observations near the system’s quadrature cannot be explained by simple symmetric disk models, but they are consistent with the shape of a Roche-lobe-filling star. We think that this is the first case of tidal deformation of a red giant being observed directly, thanks to the interferometric technique. By combining our interferometric modeling results with the analysis of the optical spectrum, multifrequency spectral energy distribution, and published radial velocities and light curves, we constrained the system parameters and show that HD 352 will likely soon enter the common envelope phase, although we cannot reject the hypothesis that it is undergoing stable mass transfer against theoretical predictions. This has important consequences for modeling a large class of binary systems. Additionally, our observations confirm that Roche-lobe-filling giants can be resolved with interferometry under favorable conditions. Such observations may help resolve the mass transfer dichotomy in systems such as symbiotic binaries, where the predominant mass transfer mode remains unclear.

中文翻译：

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通过干涉测量法明确探测双星系统中红巨星的潮汐变形


虽然双星系统中的质量传递是双星演化模型的一个关键方面，但它仍远未被理解。HD 352 是一个表现出椭球体变率的光谱双星，可能是由于潮汐变形的巨型供体填充了它的罗氏叶并将物质转移到一个微弱的伴星。在这里，我们分析了 2010 年至 2020 年间获得的系统的 VLTI/PIONIER 干涉观测数据。我们证明，系统正交附近的观测不能用简单的对称盘模型来解释，但它们与罗氏波瓣填充星的形状一致。我们认为，由于干涉测量技术，这是直接观察到红巨星潮汐变形的第一个案例。通过将我们的干涉建模结果与光谱、多频光谱能量分布以及已发布的径向速度和光曲线的分析相结合，我们限制了系统参数，并表明 HD 352 可能很快就会进入公共包络阶段，尽管我们不能拒绝它正在经历稳定传质的假设，这与理论预测相反。这对于对一大类二进制系统进行建模具有重要影响。此外，我们的观察证实，在有利条件下，可以通过干涉测量法分辨罗氏叶填充巨星。这样的观察可能有助于解决共生双星等系统中的传质二分法，其中主要的传质模式仍然不清楚。