[论文解读] TESS unveils the phase curve of WASP-33b. Characterization of the planetary atmosphere and the pulsations from the star

C. von Essen, M. Mallonn+5 more|Apr 22, 2020

Stellar, planetary, and galactic studies参考文献 89被引用 8

一句话总结

本研究利用TESS的23天光变曲线数据，首次测量了超热木星WASP-33b的光学相位曲线和二次凌日深度。在去除恒星脉动影响后，测得二次凌日深度为305.8 ± 35.5 ppm，相位曲线振幅为100.4 ± 13.1 ppm，亮度偏移为28.7 ± 7.1°，由此得出白天/夜晚温度分别为3014 ± 60 K和1605 ± 45 K，反照率（Bond albedo）为0.369 ± 0.050，热量再循环效率为0.189 ± 0.014。

ABSTRACT

We present the detection and characterization of the full-orbit phase curve and secondary eclipse of the ultra-hot Jupiter WASP-33b at optical wavelengths, along with the pulsation spectrum of the host star. We analyzed data collected by the Transiting Exoplanet Survey Satellite (TESS) in sector 18. WASP-33b belongs to a very short list of highly irradiated exoplanets that were discovered from the ground and were later visited by TESS. The host star of WASP-33b is of delta Scuti-type and shows nonradial pulsations in the millimagnitude regime, with periods comparable to the period of the primary transit. These completely deform the photometric light curve, which hinders our interpretations. By carrying out a detailed determination of the pulsation spectrum of the host star, we find 29 pulsation frequencies with a signal-to-noise ratio higher than 4. After cleaning the light curve from the stellar pulsations, we confidently report a secondary eclipse depth of 305.8 +/- 35.5 parts-per-million (ppm), along with an amplitude of the phase curve of 100.4 +/- 13.1 ppm and a corresponding westward offset between the region of maximum brightness and the substellar point of 28.7 +/- 7.1 degrees, making WASP-33b one of the few planets with such an offset found so far. Our derived Bond albedo, A_B = 0.369 +/- 0.050, and heat recirculation efficiency, epsilon = 0.189 +/- 0.014, confirm again that he behavior of WASP-33b is similar to that of other hot Jupiters, despite the high irradiation received from its host star. By connecting the amplitude of the phase curve to the primary transit and depths of the secondary eclipse, we determine that the day- and nightside brightness temperatures of WASP-33b are 3014 +/- 60 K and 1605 +/- 45 K, respectively. From the detection of photometric variations due to gravitational interactions, we estimate a planet mass of M_P = 2.81 +/- 0.53 M$_J.

研究动机与目标

• 利用TESS数据表征WASP-33b的完整轨道光学相位曲线与二次凌日特征。
• 分离恒星脉动对系外行星光变曲线的影响，以实现大气参数的精确反演。
• 基于光学测光数据测量行星的亮度温度、Bond反照率与热量再循环效率。
• 通过光变曲线的光度变化与脉动相位分析，探究潜在的恒星-行星相互作用。
• 识别并表征δ Scuti型恒星WASP-33的脉动谱，揭示新的脉动频率。

提出的方法

• 获取并处理了来自TESS第18观测段的23天WASP-33光变曲线数据。
• 进行了详细的星震学分析，识别出29个信噪比≥4的脉动频率，包括暗示存在重力模的低频模式。
• 应用脉动清理技术，在拟合行星相位曲线与凌日信号前，从光变曲线中去除恒星的变异性。
• 采用简单的热辐射模型，基于凌日深度与相位曲线振幅推导出白天与夜晚的亮度温度。
• 利用推导出的温度与凌日深度计算Bond反照率与热量再循环效率。
• 基于光变曲线的相位叠合，通过引力相互作用引起的光度变化估算行星质量。

实验结果

研究问题

• RQ1 TESS测得的WASP-33b光学相位曲线振幅与二次凌日深度分别是多少？
• RQ2 δ Scuti型恒星的脉动如何影响对系外行星光变曲线的解读？
• RQ3 基于光学相位曲线建模，WASP-33b的白天与夜晚亮度温度分别是多少？
• RQ4 WASP-33b的Bond反照率与热量再循环效率是多少？与其它热木星相比有何差异？
• RQ5 在TESS光变曲线中是否存在可探测的恒星-行星相互作用的光度特征？

主要发现

• 在TESS波段内测得的二次凌日深度为305.8 ± 35.5 ppm，表明存在强烈的热辐射。
• 相位曲线振幅为100.4 ± 13.1 ppm，峰值亮度与天顶点之间存在28.7 ± 7.1°的西向偏移。
• 推导出的白天亮度温度为3014 ± 60 K，夜晚温度为1605 ± 45 K。
• Bond反照率测定为0.369 ± 0.050，几何反照率的3σ上限为0.08，表明热辐射占主导，反射光贡献较小。
• 热量再循环效率估计为0.189 ± 0.014，与超热木星大气中H2离解/再结合过程的理论模型一致。
• 通过引力相互作用引起的光度变化，估算出行星质量为2.81 ± 0.53 M_J，与径向速度测量结果一致。