天鹅座大质量恒星的高角分辨率巡天OB2：Gemini Near-InfraRed成像仪的$JHK$自适应光学结果
A High Angular Resolution Survey of Massive Stars in Cygnus OB2: $JHK$ Adaptive Optics Results from the Gemini Near-InfraRed Imager
摘要：
我们目前的结果高角分辨率调查的大规模OB星在天鹅座OB 2协会，我们进行了与NIRI相机和ALTAIR自适应光学系统的双子座北望远镜。我们在$JHK$红外波段观测了天鹅座OB 2中的74颗O型和早期B型星，以探测双星和多星伴星。观测结果对间距小至0.08 \arcsec的等亮度双星对很敏感，而逐渐变暗的伴星在间距为2角秒的情况下可以探测到，直到$Δ$ K = 9等。由于读取噪声导致的这种微弱的对比度极限在探测器边缘附近持续到10弧秒。我们分配了一个简单的概率的机会对准每个同伴的基础上，其分离和星等差异，从中央目标恒星和面积恒星计数的一般恒星领域的天鹅座OB 2。场成员概率小于1%的伴星被认为是物理伴星。这一评估表明，47%的目标至少有一个被解析的伴星，可能是引力束缚的。包括已知的光谱双星，我们的样本包括27个二进制，12三重，和9个系统与四个或更多的组件。这些结果证实了在其他环境中的高质量恒星的研究，发现大质量恒星出生时具有高的多重性分数。这些结果对于恒星在H-R图中的位置、光谱分析的解释以及未来通过测量轨道运动来确定质量都很重要。
英文摘要：
We present results of a high angular resolution survey of massive OB stars in the Cygnus OB2 association that we conducted with the NIRI camera and ALTAIR adaptive optics system of the Gemini North telescope. We observed 74 O- and early B-type stars in Cyg OB2 in the $JHK$ infrared bands in order to detect binary and multiple companions. The observations are sensitive to equal-brightness pairs at separations as small as 0.08 \arcsec, and progressively fainter companions are detectable out to $Δ$ K = 9 mag at a separation of 2 arcsec. This faint contrast limit due to readnoise continues out to 10 arcsec near the edge of the detector. We assigned a simple probability of chance alignment to each companion based upon its separation and magnitude difference from the central target star and upon areal star counts for the general star field of Cyg OB2. Companion stars with a field membership probability of less than 1% are assumed to be physical companions. This assessment indicates that 47% of the targets have at least one resolved companion that is probably gravitationally bound. Including known spectroscopic binaries, our sample includes 27 binary, 12 triple, and 9 systems with four or more components. These results confirm studies of high mass stars in other environments that find that massive stars are born with a high multiplicity fraction. The results are important for the placement of the stars in the H-R diagram, the interpretation of their spectroscopic analyses, and for future mass determinations through measurement of orbital motion.
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