标题： 利用激光导星自适应光学发现的一个66毫角秒的超冷双星系统 显示英文标题

标题： Discovery of a 66 mas Ultracool Binary with Laser Guide Star Adaptive Optics

摘要： 我们报告了2MASS J21321145+1341584AB作为非常低质量场矮星双星的发现，它由凯克II望远镜使用激光导星自适应光学技术，在近红外波段以0.066"的分离度解析。通过分量之间的角距离以及它们共同自行运动的限制，推断出物理上的关联性。我们获得了该双星的近红外光谱，并发现它最好由一个L5±0.5主星和一个L7.5±0.5次级星描述。模型依赖的质量预测表明这两个分量跨越了氢燃烧极限阈值，其中主星可能是恒星，次级星可能是亚恒星。该系统的性质——投影分离（1.8±0.3 AU）和接近于1的质量比——与之前对于非常低质量场双星的结果一致。这个系统的相对短的估计轨道周期（~7-12年）使其成为动力学质量测量的良好目标。有趣的是，该系统的角分离是迄今为止从地面望远镜发表的任何非常低质量双星中最紧密的，也是到目前为止使用激光导星自适应光学发现的最紧密的双星。 显示英文摘要

摘要： We present the discovery of 2MASS J21321145+1341584AB as a closely separated (0.066") very low-mass field dwarf binary resolved in the near-infrared by the Keck II Telescope using laser guide star adaptive optics. Physical association is deduced from the angular proximity of the components and constraints on their common proper motion. We have obtained a near-infrared spectrum of the binary and find that it is best described by an L5+/-0.5 primary and an L7.5+/-0.5 secondary. Model-dependent masses predict that the two components straddle the hydrogen burning limit threshold with the primary likely stellar and the secondary likely substellar. The properties of this sytem - close projected separation (1.8+/-0.3 AU) and near unity mass ratio - are consistent with previous results for very low-mass field binaries. The relatively short estimated orbital period of this system (~7-12 yr) makes it a good target for dynamical mass measurements. Interestingly, the system's angular separation is the tightest yet for any very low-mass binary published from a ground-based telescope and is the tightest binary discovered with laser guide star adaptive optics to date.