Hazy with a Chance of Star Spots: Constraining the Atmosphere of Young Planet K2-33b
Hazy with a Chance of Star Spots: Constraining the Atmosphere of Young Planet K2-33b
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DOI：
10.3847/1538-3881/aca07a
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发表时间：
2022-11
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通讯作者：
P. C. Thao;A. Mann;P. Gao;Dylan A. Owens;A. Vanderburg;E. Newton;Yao Tang;M. J. Fields;T. David;J. Irwin;T. Husser;D. Charbonneau;S. Ballard
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作者：
P. C. Thao;A. Mann;P. Gao;Dylan A. Owens;A. Vanderburg;E. Newton;Yao Tang;M. J. Fields;T. David;J. Irwin;T. Husser;D. Charbonneau;S. Ballard
虽然全天空巡天已经发现了几十颗年轻的行星，但对它们的大气层知之甚少。在这里，我们提出了多波长过境数据的超海王星大小的系外行星，K2- 33 b-最年轻的（1000万年）过境系外行星的日期。我们结合了来自K2、MEarth、哈勃太空望远镜（HST）和斯皮策望远镜的K2-33的光度观测，涵盖了总共33次跨越2年的凌日。凌日测光从光学到近红外（0.6-4.5 μm），使我们能够构建行星的透射光谱。我们发现，光学渡越深度是近红外的近2倍深。这种差异适用于多年来采集的多个数据集，排除了数据分析和不受约束的系统性问题。年轻星星表面的不均匀性可以重现一些差异，但所需的斑点覆盖率（>60%）被观测到的恒星光谱（<20%）排除。我们发现一个更好的适合使用光化学雾，这是预测在年轻，中等温度，大半径的行星，如K2- 33 b强的透射光谱。一个托林霾与CO作为主要的气态碳载体在大气中可以合理地再现数据与小或没有恒星表面的不均匀性，与恒星光谱一致。HST数据质量不足以检测任何分子特征。需要更多的观测来充分表征霾和斑点特性，并确认目前数据所建议的CO的存在。
Although all-sky surveys have led to the discovery of dozens of young planets, little is known about their atmospheres. Here, we present multiwavelength transit data for the super-Neptune sized exoplanet, K2-33b—the youngest (∼10 Myr) transiting exoplanet to date. We combined photometric observations of K2-33 covering a total of 33 transits spanning >2 yr, taken from K2, MEarth, the Hubble Space Telescope (HST), and Spitzer. The transit photometry spanned from the optical to the near-infrared (0.6–4.5 μm), enabling us to construct a transmission spectrum of the planet. We find that the optical transit depths are nearly a factor of 2 deeper than those from the near-infrared. This difference holds across multiple data sets taken over years, ruling out issues of data analysis and unconstrained systematics. Surface inhomogeneities on the young star can reproduce some of the difference, but required spot coverage fractions (>60%) are ruled out by the observed stellar spectrum (<20%). We find a better fit to the transmission spectrum using photochemical hazes, which were predicted to be strong in young, moderate-temperature, and large-radius planets like K2-33b. A tholin haze with CO as the dominant gaseous carbon carrier in the atmosphere can reasonably reproduce the data with small or no stellar surface inhomogeneities, consistent with the stellar spectrum. The HST data quality is insufficient for the detection of any molecular features. More observations would be required to fully characterize the hazes and spot properties and confirm the presence of CO suggested by current data.