微透镜事件MOA-2007-BLG-400：发掘一个凉爽的木星质量行星的埋藏签名
Microlensing Event MOA-2007-BLG-400: Exhuming the Buried Signature of a Cool, Jovian-Mass Planet
摘要：
我们报告了一颗冷的木星质量的行星MOA-2007-BLG-400 Lb的探测结果。这颗行星是在一次高放大率的微透镜事件（峰值放大率A_max = 628）中被探测到的，在这次事件中，主透镜穿过了光源，导致事件的峰值戏剧性地平滑。由于行星的扰动区域的角度范围明显小于源的角度大小，因此行星特征也被有限的源大小平滑。因此，与单镜片适配的偏差较宽且相对较弱（约百分之几）。尽管如此，我们还是证明了偏离的行星性质可以从残差的总体特征中明确地确定，并且详细的分析得出了相当精确的行星/恒星质量比q = 0.0026+/-0.0004，这与探测到的大的显著性（Δχ^2=1070）是一致的。行星/恒星的投影分离受到强烈的近/宽简并的影响，导致两个不可区分的解决方案，其分离度相差约8.5倍。透镜的通量上限限制它的质量为M < 0.75 M_Sun（假设它是主序星）。一个包含了所有观测限制的贝叶斯分析表明，银河系隆起中有一颗质量约为0.2-0.5 M_太阳的恒星，因此其行星质量约为0.5-1.3 M_木星。对闭（宽）溶液，分离温度和平衡温度分别为~0.6-1.1AU（~5.3-9.7AU）和~ 103 K（~ 34 K）。如果主星是主序星，后续观测将能够探测到它的光，从而测量它的质量和距离。
英文摘要：
We report the detection of the cool, Jovian-mass planet MOA-2007-BLG-400Lb. The planet was detected in a high-magnification microlensing event (with peak magnification A_max = 628) in which the primary lens transited the source, resulting in a dramatic smoothing of the peak of the event. The angular extent of the region of perturbation due to the planet is significantly smaller than the angular size of the source, and as a result the planetary signature is also smoothed out by the finite source size. Thus the deviation from a single-lens fit is broad and relatively weak (~ few percent). Nevertheless, we demonstrate that the planetary nature of the deviation can be unambiguously ascertained from the gross features of the residuals, and detailed analysis yields a fairly precise planet/star mass ratio of q = 0.0026+/-0.0004, in accord with the large significance (Δχ^2=1070) of the detection. The planet/star projected separation is subject to a strong close/wide degeneracy, leading to two indistinguishable solutions that differ in separation by a factor of ~8.5. Upper limits on flux from the lens constrain its mass to be M < 0.75 M_Sun (assuming it is a main-sequence star). A Bayesian analysis that includes all available observational constraints indicates a primary in the Galactic bulge with a mass of ~0.2-0.5 M_Sun and thus a planet mass of ~ 0.5-1.3 M_Jupiter. The separation and equilibrium temperature are ~0.6-1.1AU (~5.3-9.7AU) and ~103K (~34K) for the close (wide) solution. If the primary is a main-sequence star, follow-up observations would enable the detection of its light and so a measurement of its mass and distance.
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