确定了AC Her的三维轨道：双星诱导的截断无法解释该post-AGB过渡盘中的大空腔
Three-dimensional orbit of AC Her determined: Binary-induced truncation cannot explain the large cavity in this post-AGB transition disk
AI总结：
本研究通过CHARA Array观测确定了post-AGB双星AC Her的首个三维天体测量轨道，发现双星动力学截断和尘埃升华半径远小于观测到的内盘空腔，从而证实大空腔更可能由环双星行星造成。
摘要：
一些演化双星，即post-asymptotic giant branch binaries，周围环绕着稳定且质量巨大的环双星盘，类似于在年轻恒星周围发现的protoplanetary disks。这些盘中大约10%是过渡盘：它们在尘埃中有一个巨大的内空腔。先前的干涉测量和建模已经排除了空腔是由尘埃升华形成的可能性，并表明空腔是由一颗巨大的环双星行星造成的，该行星将尘埃困在盘中，并导致在post-AGB恒星表面观测到难熔元素的耗竭。在本研究中，我们测试了另一种情景，即大空腔可能是由于内部双星的动力学截断造成的。我们使用CHARA Array对这种围绕post-AGB双星的过渡盘的原型：AC Her进行了近红外干涉观测。我们在4年内的10个历元探测到了伴星，并结合径向速度时间序列，利用这些天体测量数据确定了其三维轨道。这是为post-AGB双星系统构建的首个天体测量轨道。我们推导出最佳拟合轨道，其半长轴为$2.01 \pm 0.01$ mas（$2.83\pm0.08$ au），倾角为$(142.9 \pm 1.1)^\circ$，升交点经度为$(155.1 \pm 1.8)^\circ$。我们发现理论上的动力学截断和尘埃升华半径至少比观测到的内盘半径（$\sim21.5$ mas或30 au）小约$\sim3\times$。这进一步证实了此类空腔的起源是由于存在一颗环双星行星的假设。
英文摘要：
Some evolved binaries, namely post-asymptotic giant branch binaries, are surrounded by stable and massive circumbinary disks similar to protoplanetary disks found around young stars. Around 10% of these disks are transition disks: they have a large inner cavity in the dust. Previous interferometric measurements and modeling have ruled out the cavity being formed by dust sublimation and suggested that the cavity is due to a massive circumbinary planet that traps the dust in the disk and produces the observed depletion of refractory elements on the surface of the post-AGB star. In this study, we test alternative scenario in which the large cavity could be due to dynamical truncation from the inner binary. We performed near-infrared interferometric observations with the CHARA Array on the archetype of such a transition disk around a post-AGB binary: AC Her. We detect the companion at ten epochs over 4 years and determine the 3-dimensional orbit using these astrometric measurements in combination with the radial velocity time series. This is the first astrometric orbit constructed for a post-AGB binary system. We derive the best-fit orbit with a semi-major axis $2.01 \pm 0.01$ mas ($2.83\pm0.08$ au), inclination $(142.9 \pm 1.1)^\circ$ and longitude of the ascending node $(155.1 \pm 1.8)^\circ$. We find that the theoretical dynamical truncation and dust sublimation radius are at least $\sim3\times$ smaller than the observed inner disk radius ($\sim21.5$ mas or 30 au). This strengthens the hypothesis that the origin of such a cavity is due to the presence of a circumbinary planet.
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