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年轻的L型矮星2质量J11193254-1137466是一颗行星质量双星

The Young L Dwarf 2MASS J11193254-1137466 is a Planetary-Mass Binary

William M. J. Best, Michael C. Liu, Trent J. Dupuy, Eugene A. Magnier

备注：
Accepted to ApJ Letters. 8 pages, 3 figures, 2 tables
发表信息：
ApJL, 843, L4 (2017)
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摘要：

利用凯克激光导星自适应光学成像技术，我们发现了一颗0.14”（3.6天文单位）的红色低重力L7矮星2 MASS J11193254-1137466。2 MASS J11193254-1137466先前已被确定为TW Hydrae协会（TWA）的可能成员。使用我们更新的测光距离和自行，基于BANYAN II模型的运动学分析给出了82%的TWA成员的概率。在TWA的10 $\pm$ 300万年的年龄和使用热启动演化模型，2 MASS J11193254- 1137466 AB是一对$3.7^{+1.2}_{-0.9}$ $M_{\rm Jup}$褐矮星，使其成为迄今为止发现的质量最低的双星。我们估计轨道周期为$90^{+80}_{-50}$年。其中一个在$K$波段稍亮，但在$J$波段较暗，这是第一个发现的年龄如此年轻的双星，可能是一颗磁通反转双星。我们还用凯克对光谱相似的TWA L7矮星WISEA J114724.10-204021.3进行了成像，没有发现双星的迹象。我们的演化模型推导的WISEA J114724.10-204021.3的$T_{\rm eff}$估计值比2 MASS J11193254- 1137466 AB高$\approx$ 230 K，这与它们的光谱相似性不一致。这种差异表明WISEA J114724.10-204021.3实际上可能是一个质量和温度与2 MASS J11193254- 1137466 AB非常相似的紧双星，或者进一步支持年轻超冷矮星的近红外光谱是由温度和重力以外的因素形成的观点。2 MASS J11193254- 1137466 AB将是测试年轻行星质量体系中演化和大气模型的基本基准。

英文摘要：

We have discovered that the extremely red, low-gravity L7 dwarf 2MASS J11193254-1137466 is a 0.14" (3.6 AU) binary using Keck laser guide star adaptive optics imaging. 2MASS J11193254-1137466 has previously been identified as a likely member of the TW Hydrae Association (TWA). Using our updated photometric distance and proper motion, a kinematic analysis based on the BANYAN II model gives an 82% probability of TWA membership. At TWA's 10$\pm$3 Myr age and using hot-start evolutionary models, 2MASS J11193254-1137466AB is a pair of $3.7^{+1.2}_{-0.9}$ $M_{\rm Jup}$ brown dwarfs, making it the lowest-mass binary discovered to date. We estimate an orbital period of $90^{+80}_{-50}$ years. One component is marginally brighter in $K$ band but fainter in $J$ band, making this a probable flux-reversal binary, the first discovered with such a young age. We also imaged the spectrally similar TWA L7 dwarf WISEA J114724.10-204021.3 with Keck and found no sign of binarity. Our evolutionary model-derived $T_{\rm eff}$ estimate for WISEA J114724.10-204021.3 is $\approx$230 K higher than for 2MASS J11193254-1137466AB, at odds with their spectral similarity. This discrepancy suggests that WISEA J114724.10-204021.3 may actually be a tight binary with masses and temperatures very similar to 2MASS J11193254-1137466AB, or further supporting the idea that near-infrared spectra of young ultracool dwarfs are shaped by factors other than temperature and gravity. 2MASS J11193254-1137466AB will be an essential benchmark for testing evolutionary and atmospheric models in the young planetary-mass regime.

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