ON THE METHOD TO INFER AN ATMOSPHERE ON A TIDALLY LOCKED SUPER EARTH EXOPLANET AND UPPER LIMITS TO GJ 876d
ON THE METHOD TO INFER AN ATMOSPHERE ON A TIDALLY LOCKED SUPER EARTH EXOPLANET AND UPPER LIMITS TO GJ 876d
复制标题
潮汐锁定超级地球系外行星大气推断方法及GJ 876d上限
DOI：
10.1088/0004-637x/703/2/1884
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
D. Deming
中科院分区：
文献类型：
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作者：
S. Seager;D. Deming
我们开发了一种方法来推断或排除潮汐锁定的炽热超级地球是否存在大气层。大气层保留问题是一个根本性的问题，特别是对于围绕M型恒星运行的行星而言，因为这类恒星具有长时间的活跃阶段以及相应的由恒星引发的行星大气逃逸和侵蚀的可能性。没有大气层的潮汐锁定行星预计会呈现出类似朗伯体的热相位曲线，导致行星 - 恒星系统的合光随行星轨道相位而变化。我们报告了斯皮策太空望远镜的红外阵列相机（IRAC）在8μm波段对格利泽876（GJ 876）进行的连续32小时观测，在25.6秒的时间采样下，每个点达到了3.9×10⁻⁴的相对测光精度。这意味着在行星热相位曲线振幅上的3σ极限为5.13×10⁻⁵。尽管数据几乎受限于光子噪声，但我们无法确凿地推断出非凌日短周期超级地球格利泽876d是否存在大气层，也无法排除其存在大气层的可能性。我们观测的限制因素是略微活跃的主星M型恒星微小且单调的光度变化，因为由行星引起的部分正弦波与恒星的线性趋势有共同的成分。然而，对于利用詹姆斯·韦伯太空望远镜观测凌日的炽热超级地球，所提出的方法是非常有前景的，并且对于建立大气逃逸的观测约束至关重要。
We develop a method to infer or rule out the presence of an atmosphere on a tidally locked hot super Earth. The question of atmosphere retention is a fundamental one, especially for planets orbiting M stars due to the star's long-duration active phase and corresponding potential for stellar-induced planetary atmospheric escape and erosion. Tidally locked planets with no atmosphere are expected to show a Lambertian-like thermal phase curve, causing the combined light of the planet–star system to vary with planet orbital phase. We report Spitzer 8 μm IRAC observations of GJ 876 taken over 32 continuous hours and reaching a relative photometric precision of 3.9 × 10−4 per point for 25.6 s time sampling. This translates to a 3σ limit of 5.13 × 10−5 on a planet thermal phase curve amplitude. Despite the almost photon-noise-limited data, we are unable to conclusively infer the presence of an atmosphere or rule one out on the non-transiting short-period super Earth GJ 876d. The limiting factor in our observations was the miniscule, monotonic photometric variation of the slightly active host M star, because the partial sine wave due to the planet has a component in common with the stellar linear trend. The proposed method is nevertheless very promising for transiting hot super Earths with the James Webb Space Telescope and is critical for establishing observational constraints for atmospheric escape.