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arXiv 0909.4784astro-ph.SRastro-ph.IM
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M8 + M8双星2质量J22062280-2047058AB的动力学质量

Dynamical Mass of the M8+M8 Binary 2MASS J22062280-2047058AB

Trent J. Dupuy, Michael C. Liu, Brendan P. Bowler

摘要:

我们提出了凯克激光导星自适应光学成像的M8+M8二进制2 MASS J2206- 2047 AB。结合HST、Gemini-North和VLT的档案数据,我们的观测跨越了双星35年轨道周期的8.3年,我们确定了0.15(+0.05,-0.03)Msun的总动力学质量,视差误差主导了不确定性。利用测量的总质量和单个光度,图森和里昂演化模型都给出了系统的年龄为0.4(+9.6,-0.2)Gyr,这与从贝桑松银河系结构模型推导出的薄盘空间运动一致。我们的质量测量结合Tucson(Lyon)演化模型也得到了精确的有效温度,分别给出组分A和B的2660+-100 K和2640+-100 K(2550+-100 K和2530+-100 K)。这些温度与其他M8矮星的估计值(来自红外线通量法和M8质量基准LHS 2397 aA)非常一致,但大气模型拟合的近红外光谱给出了两个组分的更高温度2800+-100 K。这种适度的差异可以用大气模型中的系统误差或对系统距离(以及质量和年龄)的轻微低估来解释。我们还发现,观察到的近红外颜色和幅度不同意里昂尘埃模型预测的,给定的质量。

英文摘要:

We present Keck laser guide star adaptive optics imaging of the M8+M8 binary 2MASS J2206-2047AB. Together with archival HST, Gemini-North, and VLT data, our observations span 8.3 years of the binary's 35 year orbital period, and we determine a total dynamical mass of 0.15 (+0.05,-0.03) Msun, with the uncertainty dominated by the parallax error. Using the measured total mass and individual luminosities, the Tucson and Lyon evolutionary models both give an age for the system of 0.4 (+9.6, -0.2) Gyr, which is consistent with its thin disk space motion derived from the Besancon Galactic structure model. Our mass measurement combined with the Tucson (Lyon) evolutionary models also yields precise effective temperatures, giving 2660+-100 K and 2640+-100K (2550+-100 K and 2530+-100 K) for components A and B, respectively. These temperatures are in good agreement with estimates for other M8 dwarfs (from the infrared flux method and the M8 mass benchmark LHS 2397aA), but atmospheric model fitting of the NIR spectrum gives hotter temperatures of 2800+-100 K for both components. This modest discrepancy can be explained by systematic errors in the atmospheric models or by a slight underestimate of the distance (and thus mass and age) of the system. We also find the observed near-infrared colors and magnitudes do not agree with those predicted by the Lyon Dusty models, given the known mass.

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