DISCOVERY OF A PLANETARY-MASS COMPANION TO A BROWN DWARF IN TAURUS
DISCOVERY OF A PLANETARY-MASS COMPANION TO A BROWN DWARF IN TAURUS
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在金牛座发现棕矮星的行星质量伴星
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发表时间：
2010
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通讯作者：
K. McLeod
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作者：
K. Todorov;K. Luhman;K. McLeod
我们使用哈勃太空望远镜上的广域行星相机 2 对金牛座恒星形成区域中年轻褐矮星的亚星伴星进行了调查。在这些数据中，我们发现了一个候选伴星，预计与其中一颗棕矮星的距离为 0.″105，相当于金牛座距离 15 个天文单位。为了确定这个物体是否是伴星，我们使用双子座天文台的自适应光学系统获得了第二个时期的这对物体的图像。哈勃和双子座数据的天体测量表明，这两个物体具有相似的自行，因此很可能是伴星。根据其辐射热光度与理论演化模型预测的比较，我们估计副星的质量为 5-10 MJup。该天体表明，褐矮星的行星质量伴星可以在 τ ≲ 1 Myr 的时间尺度内形成。如此快的时间尺度上的伴星形成更有可能是通过盘中的重力不稳定或云核的碎片而不是通过核心吸积而发生。双子座图像还揭示了一颗年轻的低质量恒星可能有一个亚恒星伴星（ρ = 0.″23），该恒星距离哈勃瞄准的褐矮星为 12.″4。如果这四个物体组成一个四重系统，那么它的分层结构表明分子云核心的碎片可以产生低于 10 MJup 的伴星。
We have performed a survey for substellar companions to young brown dwarfs in the Taurus star-forming region using the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. In these data, we have discovered a candidate companion at a projected separation of 0.″105 from one of the brown dwarfs, corresponding to 15 AU at the distance of Taurus. To determine if this object is a companion, we have obtained images of the pair at a second epoch with the adaptive optics system at Gemini Observatory. The astrometry from the Hubble and Gemini data indicates that the two objects share similar proper motions and thus are likely companions. We estimate a mass of 5–10 MJup for the secondary based on a comparison of its bolometric luminosity to the predictions of theoretical evolutionary models. This object demonstrates that planetary-mass companions to brown dwarfs can form on a timescale of τ ≲ 1 Myr. Companion formation on such a rapid timescale is more likely to occur via gravitational instability in a disk or fragmentation of a cloud core than through core accretion. The Gemini images also reveal a possible substellar companion (ρ = 0.″23) to a young low-mass star that is 12.″4 from the brown dwarf targeted by Hubble. If these four objects comprise a quadruple system, then its hierarchical configuration would suggest that the fragmentation of molecular cloud cores can produce companions below 10 MJup.