VHS J125601 .92-125723.9 b的热红外成像和大气模拟：在分级三重系统中中等厚云和平衡碳化学的证据
Thermal Infrared Imaging and Atmospheric Modeling of VHS J125601.92-125723.9 b: Evidence for Moderately Thick Clouds and Equilibrium Carbon Chemistry in a Hierarchical Triple System
摘要：
我们给出并分析了附近的M矮星VHS J125601.92-125723.9（VHS 1256）的Subaru/IRCS L'和M'图像，最近声称它有一个11 M_Jup的伴星（VHS 1256 b），距离为102 au。我们的AO图像将中央恒星部分解析为双星，其组成部分的亮度几乎相等，并且分离为0.106”+/- 0.001”。VHS 1256 b占据了与HR 8799 bcde几乎相同的近红外色星等图位置，并且具有可比较的L'亮度。然而，它的H-M '颜色更红，意味着它的M'通量密度比HR 8799行星相对更亮，这表明VHS 1256 b中的非平衡碳化学可能不那么重要。我们成功地匹配了VHS 1256 b的整个SED（光学到热红外）与大气模型，假设化学平衡，模型未能重现HR 8799 b在5微米。我们的模型倾向于在伴星的大气层中有稍微厚一点的云，尽管可能没有最近HR 8799 bcde所青睐的那么厚。我们估计，该系统的年龄至少超过2亿年，组成中央双星的恒星质量至少为58兆焦耳。此外，我们发现VHS 1256的一些性质与最近关于它是AB Dor移动群成员的建议不一致。考虑到可能的距离范围（12.7 pc与17.1 pc），VHS 1256 b的质量下限范围为10.5 - 26.2 M_Jup。我们的探测极限排除了比VHS 1256 b质量更大的伴星在6-8 au外部，对第二个更大质量的伴星施加了重大限制，并提供了一些证据，这些伴星可能将宽分离伴星分散到其当前位置。VHS 1256很可能是一个质量非常低的三级系统，并且可能是第三个所有成分都属于棕矮星质量体系的三级系统。
英文摘要：
We present and analyze Subaru/IRCS L' and M' images of the nearby M dwarf VHS J125601.92-125723.9 (VHS 1256), which was recently claimed to have a ~11 M_Jup companion (VHS 1256 b) at ~102 au separation. Our AO images partially resolve the central star into a binary, whose components are nearly equal in brightness and separated by 0.106" +/- 0.001". VHS 1256 b occupies nearly the same near-IR color-magnitude diagram position as HR 8799 bcde and has a comparable L' brightness. However, it has a substantially redder H - M' color, implying a relatively brighter M' flux density than for the HR 8799 planets and suggesting that non-equilibrium carbon chemistry may be less significant in VHS 1256 b. We successfully match the entire SED (optical through thermal infrared) for VHS 1256 b to atmospheric models assuming chemical equilibrium, models which failed to reproduce HR 8799 b at 5 microns. Our modeling favors slightly thick clouds in the companion's atmosphere, although perhaps not quite as thick as those favored recently for HR 8799 bcde. We estimate that the system is at least older than 200 Myr and the masses of the stars comprising the central binary are at least 58 M_Jup each. Moreover, we find some of the properties of VHS 1256 are inconsistent with the recent suggestion that it is a member of the AB Dor moving group. Given the possible ranges in distance (12.7 pc vs. 17.1 pc), the lower mass limit for VHS 1256 b ranges from 10.5 - 26.2 M_Jup. Our detection limits rule out companions more massive than VHS 1256 b exterior to 6-8 au, placing significant limits on and providing some evidence against a second, more massive companion that may have scattered the wide-separation companion to its current location. VHS 1256 is most likely a very low mass hierarchical triple system, and could be the third such system in which all components reside in the brown dwarf mass regime.
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