利用VLTI/GRAVITY研究39颗银河系沃尔夫-拉叶星：揭示长周期双星荒漠
Investigating 39 Galactic Wolf-Rayet stars with VLTI/GRAVITY: Uncovering A Long Period Binary Desert
AI总结：
本研究利用VLTI/GRAVITY红外干涉测量调查39颗银河系沃尔夫-拉叶星，发现长周期双星稀少，与演化模型预测的200天周期峰值不符，揭示前身星可能经历不稳定质量转移导致短周期系统或并合。
摘要：
沃尔夫-拉叶星（WRs）是大质量恒星演化的最终阶段之一，也是恒星质量黑洞的直接前身。它们的多重性为预测引力波前身星的单星和双星种群模型提供了重要的锚点。最近的 spectroscopic 巡天活动表明，在短轨道周期和长轨道周期下，银河系富氮和富碳的 WRs（WNs 和 WCs）的多重性比例和周期分布存在不一致，这与演化模型预测相矛盾。在本工作中，我们利用 VLTI 上的 K 波段仪器 GRAVITY 进行红外干涉测量，以研究 WRs 在长周期下的多重性并探索其伴星的性质。我们展示了一项包含 39 颗银河系 WRs 的巡天，其中包括 11 颗 WN、15 颗 WC 和 13 颗富氢 WN（WNh）恒星。我们仅用 GRAVITY 探测到四颗恒星的宽轨道伴星：WR 48、WR 89、WR 93 和 WR 115。结合光谱学研究，我们得到了多重性比例 $f^{\rm WN}_{\rm obs} = 0.55\pm0.15$、$f^{\rm WC}_{\rm obs} = 0.40\pm0.13$ 和 $f^{\rm WNh}_{\rm obs} = 0.23\pm0.12$。此外，我们还在 GRAVITY 数据集中发现了其他特征，例如（i）超过一半的 WR 样本中存在弥散的扩展成分；（ii）在差分相位数据中解析出了五颗已知的光谱双星；以及（iii）在四颗恒星中空间分辨了星风：WR 16、WR 31a、WR 78 和 WR 110。我们的巡天揭示了缺乏中等周期（几百天）和长周期（几年到几十年）的 WR 系统。由 Case B 质量转移双星演化模型预测的 WR+OB 和 BH+OB 双星周期分布中的 200 天峰值在我们的数据中并未出现。其 O 型前身星在此分离范围内的丰富伴星关系表明，WR 前身星膨胀并与伴星相互作用，很可能通过不稳定质量转移，导致形成短周期系统或并合。
英文摘要：
Wolf-Rayet stars (WRs) are one of the final evolutionary stages of massive stars and immediate progenitors of stellar-mass black holes. Their multiplicity forms an important anchor point in single and binary population models for predicting gravitational-wave progenitors. Recent spectroscopic campaigns have suggested incompatible multiplicity fractions and period distributions for N- and C-rich Galactic WRs (WNs and WCs) at short as well as long orbital periods, in contradiction with evolutionary model predictions. In this work, we employed infrared interferometry using the $K$-band instrument GRAVITY at the VLTI to investigate the multiplicity of WRs at long periods and explore the nature of their companions. We present a survey of 39 Galactic WRs, including 11 WN, 15 WC and 13 H-rich WN (WNh) stars. We detected wide companions with GRAVITY for only four stars: WR 48, WR 89, WR 93 and WR 115. Combining with spectroscopic studies, we arrived at multiplicity fractions of $f^{\rm WN}_{\rm obs} = 0.55\pm0.15$, $f^{\rm WC}_{\rm obs} = 0.40\pm0.13$ and $f^{\rm WNh}_{\rm obs} = 0.23\pm0.12$. In addition, we also found other features in the GRAVITY dataset such as (i) a diffuse extended component in over half the WR sample; (ii) five known spectroscopic binaries resolved in differential phase data and (iii) spatially resolved winds in four stars: WR 16, WR 31a, WR 78 and WR 110. Our survey reveals a lack of intermediate (few 100s d) and long- (few years to decades) period WR systems. The 200-d peak in the period distributions of WR+OB and BH+OB binaries predicted by Case B mass-transfer binary evolution models is not seen in our data. The rich companionship of their O-type progenitors in this separation range suggest that the WR progenitor stars expand and interact with their companions, most likely through unstable mass-transfer, resulting in either a short-period system or a merger.
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