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arXiv 0908.1977astro-ph.EP
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热土星HD 149026 b的8微米相位变化

The 8 Micron Phase Variation of the Hot Saturn HD 149026b

Heather A. Knutson, David Charbonneau, Nicolas B. Cowan, Jonathan J. Fortney, Adam P. Showman, Eric Agol, Gregory W. Henry

摘要:

我们使用斯皮策太空望远镜上的红外阵列相机(IRAC)在略多于半个轨道的8.0微米处监测恒星HD 149026及其土星质量的行星。我们发现,在这段时间内,行星-恒星组合通量增加了0.0227% +/- 0.0066%(3.4 sigma显著性)。来自行星的最小通量是最大通量的45% +/- 19%,相当于两个半球之间的亮度温度差为480 +/- 140 K。我们在这个波段得到一个新的二次食深度为0.0411% +/- 0.0076%,对应于1440 +/- 150 K的昼侧亮度温度。我们新的二次日食深度是Harrington等人(2007)在同一带通中先前测量值(3.0 sigma差异)的一半。我们重新拟合了Harrington等人(2007)的数据,并获得了与我们的新值一致的较小日食深度的良好拟合。与先前的说法相反,我们新的日食深度表明,这颗行星的昼面发射光谱相对较冷,亮度温度为8微米,低于最大行星范围的平衡温度。我们测量了凌日和二次日食之间的时间间隔,发现二次日食比圆形轨道的预测提前了20.9 + 7.2/ -6.5分钟(2.9 sigma),这是一个稍微显着的结果。这对应于e*cos(omega)= -0.0079 +0.0027 / -0.0025其中e是行星的轨道偏心率,omega是近心角。

英文摘要:

We monitor the star HD 149026 and its Saturn-mass planet at 8.0 micron over slightly more than half an orbit using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We find an increase of 0.0227% +/- 0.0066% (3.4 sigma significance) in the combined planet-star flux during this interval. The minimum flux from the planet is 45% +/- 19% of the maximum planet flux, corresponding to a difference in brightness temperature of 480 +/- 140 K between the two hemispheres. We derive a new secondary eclipse depth of 0.0411% +/- 0.0076% in this band, corresponding to a dayside brightness temperature of 1440 +/- 150 K. Our new secondary eclipse depth is half that of a previous measurement (3.0 sigma difference) in this same bandpass by Harrington et al. (2007). We re-fit the Harrington et al. (2007) data and obtain a comparably good fit with a smaller eclipse depth that is consistent with our new value. In contrast to earlier claims, our new eclipse depth suggests that this planet's dayside emission spectrum is relatively cool, with an 8 micron brightness temperature that is less than the maximum planet-wide equilibrium temperature. We measure the interval between the transit and secondary eclipse and find that that the secondary eclipse occurs 20.9 +7.2 / -6.5 minutes earlier (2.9 sigma) than predicted for a circular orbit, a marginally significant result. This corresponds to e*cos(omega) = -0.0079 +0.0027 / -0.0025 where e is the planet's orbital eccentricity and omega is the argument of pericenter.

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