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arXiv 1202.3829astro-ph.EP
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朝向遥远世界的一致映射:系外行星HD189733b的二次日食扫描

Towards consistent mapping of distant worlds: secondary-eclipse scanning of the exoplanet HD189733b

Julien de Wit, Michaël Gillon, Brice-Olivier Demory, Sara Seager

摘要:

绘制遥远世界的地图是系外行星红外测光研究的下一个前沿。最终,限制系外行星大气层的空间和时间特性将为其物理学提供进一步的见解。对于潮汐锁定的热彗星,过境和被他们的主恒星黯然失色,第一步现在是可能的。我们的目标是约束系外行星的形状,亮度分布(BD)和系统参数从它的光变曲线。值得注意的是,我们依靠日食扫描。我们使用HD 189733的存档Spitzer 8 μm数据(6次凌日,8次日食和一条相位曲线)在全球MCMC程序中减轻系统学。我们还包括HD 189733的出过境径向速度测量。我们发现一个6 σ偏离预期的掩星均匀明亮的磁盘。这种偏差主要来自HD 189733 b的热模式,而不是它的形状。我们指出轨道偏心率e和BD(均匀时间偏移)的相关性也依赖于恒星密度ρ* 和碰撞参量b(e-b-ρ*-BD相关性)。对于HD 189733 b,我们发现放松e约束并使用更复杂的BD会导致恒星/行星密度更低,以及更局部化和纬度变化的热点。当包含RV测量时,我们得到了一个改进的HD 189733 b轨道偏心率上限的约束,e<0.011(95%)。我们的研究为分析系外行星光变曲线提供了新的见解,并为未来的日食扫描观测提供了适当的框架。在不同波长下对同一颗系外行星的观测将改善其系统参数的约束,同时最终产生其大气层的大规模时间依赖3D地图。最后,我们讨论了我们的方法在可见光观测的角度,特别是为了更好地了解系外行星hapdos。

英文摘要:

Mapping distant worlds is the next frontier for exoplanet infrared photometry studies. Ultimately, constraining spatial and temporal properties of an exoplanet atmosphere will provide further insight into its physics. For tidally-locked hot Jupiters that transit and are eclipsed by their host star, the first steps are now possible. Our aim is to constrain an exoplanet's shape, brightness distribution (BD) and system parameters from its light curve. Notably, we rely on the eclipse scanning. We use archived Spitzer 8-μm data of HD189733 (6 transits, 8 secondary eclipses, and a phase curve) in a global MCMC procedure for mitigating systematics. We also include HD189733's out-of-transit radial velocity measurements. We find a 6-σ deviation from the expected occultation of a uniformly-bright disk. This deviation emerges mainly from HD189733b's thermal pattern, not from its shape. We indicate that the correlation of the orbital eccentricity, e, and BD (uniform time offset) does also depend on the stellar density, ρ*, and the impact parameter, b (e-b-ρ*-BD correlation). For HD189733b, we find that relaxing the e-constraint and using more complex BDs lead to lower stellar/planetary densities and a more localized and latitudinally-shifted hot spot. We obtain an improved constraint on the upper limit of HD189733b's orbital eccentricity, e<0.011 (95%), when including the RV measurements. Our study provides new insights into the analysis of exoplanet light curves and a proper framework for future eclipse-scanning observations. Observations of the same exoplanet at different wavelengths will improve the constraints on its system parameters while ultimately yielding a large-scale time-dependent 3D map of its atmosphere. Finally, we discuss the perspective of extending our method to observations in the visible, in particular to better understand exoplanet albedos.

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