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arXiv 0904.0249astro-ph.GA
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极端微透镜事件OGLE-2007-BLG-224：厚盘棕矮星的陆地视差观测

The Extreme Microlensing Event OGLE-2007-BLG-224: Terrestrial Parallax Observation of a Thick-Disk Brown Dwarf

A. Gould, A. Udalski, B. Monard, K. Horne, Subo Dong, N. Miyake, K. Sahu, D. P. Bennett, the OGLE, MicroFUN, RoboNet, MOA, PLANET collaborations

备注：
ApJ Letters, in press, 15 pages including 2 figures
发表信息：
Astrophys.J.698:L147-L151,2009
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摘要：

视差是测量天体距离的最基本技术。虽然地球视差是2000多年前由喜帕恰斯（约。由于地球的基线非常小，因此地球视差通常只能应用于太阳系中的物体。然而，存在一类极端的引力微透镜事件，其中地球视差的影响可以很容易地检测到，因此允许测量的距离，质量和横向速度的镜头。在这里，我们报告了第一个这样的极端微透镜事件OGLE-2007-BLG-224的观测结果，从中我们推断该透镜是一颗质量为M=0.056 +- 0.004 Msun的褐矮星，距离为525 +- 40 pc，横向速度为113 +- 21 km/s。速度将透镜置于厚盘中，使其成为迄今为止探测到的质量最低的厚盘棕矮星。后续观测可能会让人们观察到来自棕矮星本身的光，从而成为这些物体进化模型的重要约束，并可能打开亚恒星物体的新窗口。在这一事件中探测到厚盘棕矮星的先验概率较低，当与其他观测的额外证据相结合时，表明旧的亚恒星物体可能比以前假设的更常见。

英文摘要：

Parallax is the most fundamental technique to measure distances to astronomical objects. Although terrestrial parallax was pioneered over 2000 years ago by Hipparchus (ca. 140 BCE) to measure the distance to the Moon, the baseline of the Earth is so small that terrestrial parallax can generally only be applied to objects in the Solar System. However, there exists a class of extreme gravitational microlensing events in which the effects of terrestrial parallax can be readily detected and so permit the measurement of the distance, mass, and transverse velocity of the lens. Here we report observations of the first such extreme microlensing event OGLE-2007-BLG-224, from which we infer that the lens is a brown dwarf of mass M=0.056 +- 0.004 Msun, with a distance of 525 +- 40 pc and a transverse velocity of 113 +- 21 km/s. The velocity places the lens in the thick disk, making this the lowest-mass thick-disk brown dwarf detected so far. Follow-up observations may allow one to observe the light from the brown dwarf itself, thus serving as an important constraint for evolutionary models of these objects and potentially opening a new window on sub-stellar objects. The low a priori probability of detecting a thick-disk brown dwarf in this event, when combined with additional evidence from other observations, suggests that old substellar objects may be more common than previously assumed.

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