论文标题
ups！...我又做了一次：揭开Upsilon Sagittarii的隐藏伴侣，这是第二个质量转移阶段的独特二进制系统
Ups!... I did it again: unveiling the hidden companion in Upsilon Sagittarii, a unique binary system at a second mass transfer stage
论文作者
论文摘要
Upsilon Sagittarii是一种缺乏氢的二进制，在初级膨胀成为核心氦气耗尽后成为氦超级巨人之后，已建议处于传质的第二阶段。对紫外线中微弱伴侣的初步识别导致对这两个组件的质量估计，使氦气中的氦气星成为IB/C型超新星的原型直接祖细胞。但是，尚未实现复杂频谱的一致模型，对这种解释产生了怀疑。在本研究中，我们首次提供适合紫外线数据的复合光谱模型，并清楚地将伴侣识别为迅速旋转的缓慢移动〜7msun B型星，与以前建议的不同。剥离的氦超巨人比以前的估计值少，并且估计质量小于1MSUN，被排除为核心偏离的超新星祖细胞。我们提供了一个详细的二进制演化方案，该方案解释了两个成分的温度和亮度以及非常低的重力（log g〜1.0 [cm/s^2]）和一级（大气质量分数xH〜0.001）的极端氢缺乏。最合适的模型是〜5msun中间质量主要的轨道时期，其初始轨道周期为几天，尽管旋转较高，但次级似乎已经获得了相当大的质量。我们得出的结论是，Upsilon Sagittarii是测试二进制进化过程的关键系统，尤其是信封剥离和质量积聚。
Upsilon Sagittarii is a hydrogen-deficient binary that has been suggested to be in its second stage of mass transfer, after the primary has expanded to become a helium supergiant following core helium exhaustion. A tentative identification of the faint companion in the ultraviolet led to mass estimates of both components that made the helium star in Upsilon Sagittarii a prototypical immediate progenitor of a type Ib/c supernova. However, no consistent model for the complex spectrum has been achieved, casting doubt on this interpretation. In the present study we provide for the first time a composite spectral model that fits the ultraviolet data, and clearly identifies the companion as a rapidly rotating slowly moving ~7Msun B-type star, unlike previously suggested. The stripped helium supergiant is less luminous than previous estimates, and, with an estimated mass smaller than 1Msun, is ruled out as a core-collapse supernova progenitor. We provide a detailed binary evolution scenario that explains the temperature and luminosity of the two components as well as the very low gravity (log g ~ 1.0 [cm/s^2]) and extreme hydrogen deficiency of the primary (atmospheric mass fraction XH ~ 0.001). The best-fitting model is a ~5Msun intermediate-mass primary with an initial orbital period of a few days, and a secondary that appears to have gained a significant amount of mass despite its high rotation. We conclude that Upsilon Sagittarii is a key system for testing binary evolution processes, especially envelope stripping and mass accretion.
