Binary interactions have been proposed to explain a variety of circumstellar structures seen around evolved stars, including asymptotic giant branch (AGB) stars and planetary nebulae. Studies resolving the circumstellar envelopes of AGB stars have revealed spirals, disks and bipolar outflows, with shaping attributed to interactions with a companion. Here we use a combined chemical and dynamical analysis to reveal a highly eccentric and long-period orbit for W Aquilae, a binary system containing an AGB star and a main-sequence companion. Our results are based on anisotropic SiN emission, the detections of irregular NS and SiC emission towards the S-type star, and density structures observed in the CO emission. These features are all interpreted as having formed during periastron interactions. Our astrochemistry-based method can yield stringent constraints on the orbital parameters of long-period binaries containing AGB stars, and will be applicable to other systems.

人们提出双星相互作用来解释演化恒星周围的各种星周结构，包括渐近巨星分支（AGB）恒星和行星状星云。解析 AGB 恒星的星周包层的研究揭示了螺旋、圆盘和双极流出，其形状归因于与伴星的相互作用。在这里，我们结合化学和动力学分析来揭示 W Aquilae 的高偏心率和长周期轨道，W Aquilae 是一个包含 AGB 恒星和主序伴星的双星系统。我们的结果基于各向异性 SiN 发射、对 S 型恒星的不规则 NS 和 SiC 发射的检测以及在 CO 发射中观察到的密度结构。这些特征都被解释为是在近星体相互作用过程中形成的。我们基于天体化学的方法可以对包含 AGB 恒星的长周期双星的轨道参数产生严格的约束，并将适用于其他系统。