A brown dwarf orbiting an M-dwarf: MOA 2009-BLG-411L
A brown dwarf orbiting an M-dwarf: MOA 2009-BLG-411L
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绕 M 矮星运行的褐矮星：MOA 2009-BLG-411L
DOI：
10.1051/0004-6361/201219765
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发表时间：
2012
影响因子：
6.5
通讯作者：
et al.,
中科院分区：
文献类型：
--
作者：
Bachelet;E.;et al.,
背景焦散交叉是微透镜中二元透镜最明显的特征。在目前的情况下，这一特征被大源星冲淡了，但经过详细的分析，可以提取伴随信号。2009年8月5日，MOA-Collaboration探测到了AimsMOA 2009-BLG-411。作为高倍率事件的警报，它对行星很敏感。光曲线中的可疑异常没有得到实时模型的证实，但进一步的分析发现，与单个透镜扩展光源拟合的偏差很小。方法由于所有合作伙伴的观察，这次事件得到了很好的监测。我们首先决定用一种比经典方法更精细的方法来表征源星的性质：我们测量了五个不同通带(VIJHK)沿视线的星际吸收。其次，我们使用标准的技术对光照曲线进行建模：生成(S，Q，α)网格以寻找局部极小值，并使用下坡法(马尔科夫链蒙特卡罗)对结果进行精化。结果我们发现源星是一颗半径为9R⊙的巨型G型星。网格搜索给出了两个局部极小值，它们对应于理论简并度≡S-1。我们发现，该透镜是由一颗质量为MS=0.05m的褐矮星围绕着质量为Mp=0.18m⊙的初级M星运行的。我们还揭示了近双星中心焦散的一种新的质量比简并。结论据我们所知，这是第一次使用微透镜技术探测我们银河系中由一颗M星和一颗棕矮星组成的双星系统。
ContextCaustic crossing is the clearest signature of binary lenses in microlensing. In the present context, this signature is diluted by the large source star but a detailed analysis has allowed the companion signal to be extracted.AimsMOA 2009-BLG-411 was detected on August 5, 2009 by the MOA-Collaboration. Alerted as a high-magnification event, it was sensitive to planets. Suspected anomalies in the light curve were not confirmed by a real-time model, but further analysis revealed small deviations from a single lens extended source fit.MethodsThanks to observations by all the collaborations, this event was well monitored. We first decided to characterize the source star properties by using a more refined method than the classical one: we measure the interstellar absorption along the line of sight in five different passbands (VIJHK). Secondly, we model the lightcurve by using the standard technique: make (s,q,α) grids to look for local minima and refine the results by using a downhill method (Markov chain Monte Carlo). Finally, we use a Galactic model to estimate the physical properties of the lens components.ResultsWe find that the source star is a giant G star with radius 9R⊙. The grid search gives two local minima, which correspond to the theoretical degeneracys≡s-1. We find that the lens is composed of a brown dwarf secondary of massMS= 0.05M⊙orbiting a primary M-star of massMP= 0.18M⊙. We also reveal a new mass-ratio degeneracy for the central caustics of close binaries.ConclusionsAs far as we are aware, this is the first detection using the microlensing technique of a binary system in our Galaxy composed of an M-star and a brown dwarf.