用HST/WFC3研究Kepler-13 Ab非反转发射光谱中大气冷阱过程的证据
Evidence for Atmospheric Cold-trap Processes in the Noninverted Emission Spectrum of Kepler-13Ab Using HST/WFC3
摘要：
我们在UT 2014年4月28日和UT 2014年10月13日使用哈勃太空望远镜上的宽视场相机3在近红外线上观察了开普勒-13 A行星系的两次日食。通过使用附近的双星Kepler-13 BC作为参考，我们能够创建Kepler-13 A的差分光变曲线，该曲线几乎没有HST/WFC 3分光光度法中通常存在的系统学。我们测量的宽带（1.1 $μ$ m至1.65 $μ$ m）的食深为$734\pm28$ ppm，并且能够测量行星在$R\approx50$的发射光谱，平均精度为70 ppm。我们发现Kepler-13 Ab具有一个非倒置的，单调下降的垂直温度分布。我们排除了等温曲线和大于3 $σ$的倒置曲线。我们还发现，在类似的有效温度下，Kepler-13 Ab的昼侧发射似乎与孤立的M7棕矮星相似。由于开普勒-13Ab相对较高的质量和表面重力，我们认为明显缺乏反转是由于行星大气中的冷阱过程。使用一个玩具模型的冷阱应该抑制反转，和其他行星的观测在这个温度范围内与测量的发射光谱，我们认为，更详细的建模和更多的观察，我们可能能够放置有用的约束的大小上的冷凝物的热彗星的向阳面。
英文摘要：
We observed two eclipses of the Kepler-13A planetary system, on UT 2014 April 28 and UT 2014 October 13, in the near-infrared using Wide Field Camera 3 on the Hubble Space Telescope. By using the nearby binary stars Kepler-13BC as a reference, we were able to create a differential light curve for Kepler-13A that had little of the systematics typically present in HST/WFC3 spectrophotometry. We measure a broadband (1.1$μ$m to 1.65$μ$m) eclipse depth of $734\pm28$ ppm, and are able to measure the emission spectrum of the planet at $R\approx50$ with an average precision of 70 ppm. We find that Kepler-13Ab possesses a noninverted, monotonically decreasing vertical temperature profile. We exclude an isothermal profile and an inverted profile at more than 3$σ$. We also find that the dayside emission of Kepler-13Ab appears generally similar to an isolated M7 brown dwarf at a similar effective temperature. Due to the relatively high mass and surface gravity of Kepler-13Ab, we suggest that the apparent lack of an inversion is due to cold-trap processes in the planet's atmosphere. Using a toy model for where cold-traps should inhibit inversions, and observations of other planets in this temperature range with measured emission spectra, we argue that with more detailed modeling and more observations we may be able to place useful constraints on the size of condensates on the daysides of hot Jupiters.
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