A Six Year, Low-resolution, Multibroadband Transit Photometry Study of HD 189733b
A Six Year, Low-resolution, Multibroadband Transit Photometry Study of HD 189733b
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DOI：
10.3847/1538-3881/ac9d37
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发表时间：
2022-12
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通讯作者：
Cristilyn N. Gardner-Watkins;H. Kobulnicky;H. Jang-Condell;D. Kasper;B. Parker;Ted Bucci;Evan M. Cook;Kaitlin A. Doublestein;Cade Freels;Dax G. T. Galloway;Sabrina Helck;Corinne Komlodi;Michael J. Lindman;McKell Lyon;A. Piccone;Samantha Wilkerson
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作者：
Cristilyn N. Gardner-Watkins;H. Kobulnicky;H. Jang-Condell;D. Kasper;B. Parker;Ted Bucci;Evan M. Cook;Kaitlin A. Doublestein;Cade Freels;Dax G. T. Galloway;Sabrina Helck;Corinne Komlodi;Michael J. Lindman;McKell Lyon;A. Piccone;Samantha Wilkerson
透射光谱学为描述系外行星的大气提供了宝贵的机会。我们提出了热木星HD 189733 b的新的地面光学透射光谱，这些光谱来自于使用近同时u′g′r′i′宽带观测在六年时间跨度（2016-2021）内观测到的九次凌日。通过在2.3 m的怀俄明州红外天文台望远镜的主焦点光谱仪上实施光学漫射器，我们实现了435（280）ppm的平均（最佳）精度。这些数据提供了新的测量表观行星半径相对于恒星半径，大气不透明度的光谱指数，和时间变化的两个数量。我们的研究结果表明，增强的光谱斜率在光学制度比预期的典型瑞利散射陡2.4倍，这是与早期的测量超瑞利斜率（SRS）。虽然恒星活动对透射光谱的影响使光谱斜率的测量变得复杂，但我们六年多的多历元数据集可以测量并平均恒星变化，得到平均光谱指数为−9.9 ± 4.4。HD 189733 b的1200 K平衡温度使其处于SRS形成的最佳点，并且与大气中的烟雾剧烈混合一致。此外，我们发现在两次凌日期间光变曲线的深度发生了变化，这可以解释为2021年6月期间被遮蔽的星星斑点的增加。虽然这颗星星是活跃的，但在我们六年的观测中，恒星活动的平均水平似乎没有显著变化，这使我们得出结论，恒星活动的变化最多是适度的。
Transmission spectroscopy offers an invaluable opportunity to characterize the atmospheres of exoplanets. We present new ground-based optical transmission spectra of the hot Jupiter HD 189733b, derived from nine transits observed over a six year time span (2016–2021) using near-simultaneous u′g′r′i′ broadband observations. We achieve an average (best) precision of 435 (280) ppm by implementing an optical diffuser on the prime focus spectrograph from the 2.3 m Wyoming Infrared Observatory telescope. The data provide new measurements of the apparent planetary radius with respect to the stellar radius, the spectral index of atmospheric opacity, and the time variability of the two quantities. Our results indicate an enhanced spectral slope in the optical regime ≈2.4 times steeper than would be expected from canonical Rayleigh scattering and that is consistent with earlier measurements of a super-Rayleigh slope (SRS). While the effect of stellar activity on the transmission spectrum complicates the measurement of the spectral slope, our multiepoch data set over six years can measure and average over stellar variations, yielding a mean spectral index of −9.9 ± 4.4. The 1200 K equilibrium temperature of HD 189733b places it in a sweet spot for the formation of SRSs and is consistent with vigorously mixing hazes in the atmosphere. Additionally, we find variations in the depth of the lightcurve during two of the transits, explainable as an increase in occulted star spots during June 2021. Although the star is active, the mean level of stellar activity does not seem to vary dramatically over our six years of observations, leading us to conclude that the variability in stellar activity is modest at most.