A JWST NIRSpec Phase Curve for WASP-121b: Dayside Emission Strongest Eastward of the Substellar Point and Nightside Conditions Conducive to Cloud Formation
A JWST NIRSpec Phase Curve for WASP-121b: Dayside Emission Strongest Eastward of the Substellar Point and Nightside Conditions Conducive to Cloud Formation
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WASP-121b 的 JWST NIRSpec 相位曲线：日侧发射最强的亚恒星点东部和夜侧条件有利于云的形成
DOI：
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发表时间：
2023
影响因子：
7.9
通讯作者：
Z. Rustamkulov
中科院分区：
文献类型：
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作者：
T. Mikal;D. Sing;Jiayin Dong;D. Foreman;T. Kataria;J. Barstow;J. Goyal;N. Lewis;J. Lothringer;N. Mayne;H. Wakeford;D. Christie;Z. Rustamkulov
我们提出了第一个系外行星的相位曲线测量与JWST NIRSpec仪器，突出了这个新委托的天文台系外行星气候研究的特殊稳定性。WASP-121 b是一颗轨道周期为30.6小时的超热木星，我们分析了NRS 1和NRS 2探测器产生的两条宽带光变曲线，波长范围分别为2.70-3.72 μm和3.82-5.15 μm。两个光变曲线都表现出最小的系统性，在30 ppm hr−1（NRS 1）和10 ppm hr−1（NRS 2）的基线通量水平上近似线性漂移。假设一个简单的亮度图为一个低阶球谐偶极子描述的行星，我们的光曲线拟合表明，相位曲线的峰值与轨道相位3.°36 ± 0.°11（NRS 1）和2.°66 ± 0.°12（NRS 2）在月食中期之前相一致。这与从亚恒星点以东发出的最强昼侧发射相一致。我们测量到的行星-星星发射比为3924 ± 7 ppm（NRS 1）和4924 ± 9 ppm（NRS 2）的昼侧半球和136 ± 8 ppm（NRS 1）和630 ± 10 ppm（NRS 2）的夜侧半球。后一个的夜面辐射比转化为行星的亮度温度为926 ± 12 K（NRS 1）和1122 ± 10 K（NRS 2），这足以形成各种各样的难熔凝析物，包括顽火辉石和镁橄榄石。夜面云层可能会阻挡来自更深、更热的大气层的排放，这可能有助于解释为什么无云3D大气环流模型模拟系统地高估了WASP-121 b的夜面排放。
We present the first exoplanet phase-curve measurement made with the JWST NIRSpec instrument, highlighting the exceptional stability of this newly commissioned observatory for exoplanet climate studies. The target, WASP-121b, is an ultrahot Jupiter with an orbital period of 30.6 hr. We analyze two broadband light curves generated for the NRS1 and NRS2 detectors, covering wavelength ranges of 2.70–3.72 μm and 3.82–5.15 μm, respectively. Both light curves exhibit minimal systematics, with approximately linear drifts in the baseline flux level of 30 ppm hr−1 (NRS1) and 10 ppm hr−1 (NRS2). Assuming a simple brightness map for the planet described by a low-order spherical harmonic dipole, our light-curve fits suggest that the phase curve peaks coincide with orbital phases 3.°36 ± 0.°11 (NRS1) and 2.°66 ± 0.°12 (NRS2) prior to mideclipse. This is consistent with the strongest dayside emission emanating from eastward of the substellar point. We measure planet-to-star emission ratios of 3924 ± 7 ppm (NRS1) and 4924 ± 9 ppm (NRS2) for the dayside hemisphere and 136 ± 8 ppm (NRS1) and 630 ± 10 ppm (NRS2) for the nightside hemisphere. The latter nightside emission ratios translate to planetary brightness temperatures of 926 ± 12 K (NRS1) and 1122 ± 10 K (NRS2), which are low enough for a wide range of refractory condensates to form, including enstatite and forsterite. A nightside cloud deck may be blocking emission from deeper, hotter layers of the atmosphere, potentially helping to explain why cloud-free 3D general circulation model simulations systematically overpredict the nightside emission for WASP-121b.