W Serpentis is an eclipsing binary system and the prototype of the Serpentid class of variable stars. These are interacting binaries experiencing intense mass transfer and mass loss. However, the identities and properties of both stars in W Ser remain a mystery. Here, we present an observational analysis of high-quality, visible-band spectroscopy made with the Apache Point Observatory 3.5 m telescope and Astrophysical Research Consortium Echelle Spectrograph spectrograph plus the first near-IR, long-baseline interferometric observations obtained with the Center for High Angular Resolution Astronomy Array. We present examples of the appearance and radial velocities of the main spectral components: prominent emission lines, strong shell absorption lines, and weak absorption lines. We show that some of the weak absorption features are associated with the cool mass donor, and we present the first radial velocity curve for the donor star. The donor’s absorption lines are rotationally broadened, and we derive a ratio of donor to gainer mass of 0.36 ± 0.09 based on the assumptions that the donor fills its Roche lobe and that it rotates synchronously with the orbit. We use a fit of the All-Sky Automated Survey light curve to determine the orbital inclination and mass estimates of 2.0M⊙ and 5.7M⊙ for the donor and gainer, respectively. The partially resolved interferometric measurements of orbital motion are consistent with our derived orbital properties and the distance from Gaia EDR3. Spectroscopic evidence indicates that the gainer is enshrouded in an opaque disk that channels the mass transfer stream into an outflow through the L3 region and into a circumbinary disk.

中文翻译：

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W 蛇形星的光谱和干涉研究。I. 相互作用的二进制 W Serpentis 中的外接二元流出


蛇形西星是一个黯然失色的双星系统，也是蛇形变星的原型。这些是相互作用的双星，经历着强烈的传质和质量损失。然而，W Ser 中两位明星的身份和属性仍然是一个谜。在这里，我们介绍了使用 Apache Point Observatory 3.5 m 望远镜和天体物理研究联盟 Echelle Spectrograph 光谱仪以及使用高角分辨率天文阵列中心获得的首次近红外、长基线干涉观测进行的高质量可见波段光谱的观测分析。我们提供了主要光谱分量的外观和径向速度的示例：突出的发射线、强壳吸收线和弱吸收线。我们表明一些弱吸收特征与冷质量供体有关，并提出了供体星的第一条径向速度曲线。供体的吸收线是旋转展宽的，我们得出供体与增益体质量的比率为 0.36 ± 0.09，基于供体填充其 Roche 叶并且它与轨道同步旋转的假设。我们使用全天空自动巡天光曲线的拟合来确定供体和增益体的轨道倾角和质量估计分别为 2.0M⊙ 和 5.7M⊙。轨道运动的部分分辨干涉测量与我们得出的轨道特性和与 Gaia EDR3 的距离一致。光谱证据表明，增益器被包裹在一个不透明的盘中，该盘将传质流引导到通过 L3 区域的流出中，并进入环二元盘。