MOA-2007-BLG-197: Exploring the brown dwarf desert
MOA-2007-BLG-197: Exploring the brown dwarf desert
复制标题
MOA-2007-BLG-197：探索棕矮星沙漠
DOI：
10.1051/0004-6361/201525791
复制
发表时间：
2015
影响因子：
6.5
通讯作者：
et al.
中科院分区：
文献类型：
--
作者：
Ranc;C.;et al.
我们介绍了对 MOA-2007-BLG-197Lb 的分析，MOA-2007-BLG-197Lb 是通过引力微透镜检测到的类太阳恒星的第一颗褐矮星伴星。 PLANET、MOA 和 μFUN 合作的望远镜网络对该事件进行了警报和光度跟踪，并使用 VLT 的 NaCo 仪器以高角分辨率进行观测。通过微透镜光变曲线的建模，我们推导出了爱因斯坦半径单位的二元透镜间距（s≃ 1.13）、质量比q=（4.732±0.020）×10-2和爱因斯坦半径穿越时间（tE≃ 82 d）等基本参数。由于时间尺度较长，我们考虑了模型中透镜的年度视差和轨道运动，以及在源焦散出口期间清晰检测到的有限源效应。为了恢复透镜系统的物理参数，我们将所得的光曲线最佳拟合参数与使用 VLT NaCo 获得的 (J,H,Ks) 幅度相结合，并使用 IRSF 和 2MASS 数据进行校准。根据该分析，我们得出透镜总质量为 0.86 ± 0.04M⊙，透镜距离 DL= 4.2 ± 0.3 kpc。我们发现 MOA-2007-BLG-197L 的伴星是一颗 41 ± 2MJo 的褐矮星，观测到的预计距离为 a⊥= 4.3 ± 0.1 AU，并绕着一颗 0.82 ± 0.04M⊙G-K 矮星运行。然后，我们将 MOA-2007-BLG-197L 的伴星放入质量周期图中，该图由迄今为止通过不同技术检测到的所有褐矮星伴星组成，包括微透镜、凌日、径向速度和直接成像（这些天体大多数围绕太阳型恒星运行）。为了研究这个种群的统计特性，我们对数据进行了二维非参数概率密度分布拟合，绘制了结构化的褐矮星景观。我们确认了存在一个在短周期和中等质量（P≲ 30 d，M~ 30−60MJ）的天体强烈耗尽的区域，但也发现了在P~ 500 d和M~ 20MJ周围的天体积累，以及另一个在长轨道周期（P≳ 500 d）和高质量（M≳ 50MJ）的耗尽区域。虽然这些数据为形成棕矮星沙漠的不同物理机制（或破坏）提供了重要线索，但还需要更多数据来确定它们的相对重要性，特别是作为主恒星质量的函数。未来的微透镜勘测应该很快就会提供更多的探测结果，特别是对于红矮星宿主，从而独特地补充太阳型宿主样本。
We present the analysis of MOA-2007-BLG-197Lb, the first brown dwarf companion to a Sun-like star detected through gravitational microlensing. The event was alerted and followed-up photometrically by a network of telescopes from the PLANET, MOA, andμFUN collaborations, and observed at high angular resolution using the NaCo instrument at the VLT. From the modelling of the microlensing light curve, we derived basic parameters such as, the binary lens separation in Einstein radius units (s≃ 1.13), the mass ratioq= (4.732 ± 0.020) × 10-2and the Einstein radius crossing time (tE≃ 82 d). Because of this long time scale, we took annual parallax and orbital motion of the lens in the models into account, as well as finite source effects that were clearly detected during the source caustic exit. To recover the lens system’s physical parameters, we combined the resulting light curve best-fit parameters with (J,H,Ks) magnitudes obtained with VLT NaCo and calibrated using IRSF and 2MASS data. From this analysis, we derived a lens total mass of 0.86 ± 0.04M⊙and a lens distance ofDL= 4.2 ± 0.3 kpc. We find that the companion of MOA-2007-BLG-197L is a brown dwarf of 41 ± 2MJobserved at a projected separation ofa⊥= 4.3 ± 0.1 AU, and orbits a 0.82 ± 0.04M⊙G-K dwarf star. We then placed the companion of MOA-2007-BLG-197L in a mass-period diagram consisting of all brown dwarf companions detected so far through different techniques, including microlensing, transit, radial velocity, and direct imaging (most of these objects orbit solar-type stars). To study the statistical properties of this population, we performed a two-dimensional, non-parametric probability density distribution fit to the data, which draws a structured brown dwarf landscape. We confirm the existence of a region that is strongly depleted in objects at short periods and intermediate masses (P≲ 30 d,M~ 30−60MJ), but also find an accumulation of objects aroundP~ 500 d andM~ 20MJ, as well as another depletion region at long orbital periods (P≳ 500 d) and high masses (M≳ 50MJ). While these data provide important clues on the different physical mechanisms of formation (or destruction) that shape the brown dwarf desert, more data are needed to establish their relative importance, in particular as a function of host star mass. Future microlensing surveys should soon provide more detections, in particular for red dwarf hosts, thus uniquely complementing the solar-type host sample.