Direct imaging of widely separated exoplanets from space will obtain their reflected light spectra and measure atmospheric properties. Previous calculations have shown that a change in the orbital phase would cause a spectral signal, but whether this signal may be used to characterize the atmosphere has not been shown. We simulate starshade-enabled observations of the planet 47 UMa b, using the present most realistic simulator Starshade Imaging Simulation Toolkit for Exoplanet Reconnaissance to estimate the uncertainties due to residual starlight, solar glint, and exozodiacal light. We then use the Bayesian retrieval algorithm EXOREL^R to determine the constraints on the atmospheric properties from observations using a Roman- or Habitable Exoplanet Observatory (HabEx)-like telescope, comparing the strategies to observe at multiple orbital phases or in multiple wavelength bands. With a ~20% bandwidth in 600–800 nm on a Roman-like telescope, the retrieval finds a degenerate scenario with a lower gas abundance and a deeper or absent cloud than the truth. Repeating the observation at a different orbital phase or at a second 20% wavelength band in 800–1000 nm, with the same integration time and thus degraded signal-to-noise ratio (S/N), would effectively eliminate this degenerate solution. Single observation with a HabEx-like telescope would yield high-precision constraints on the gas abundances and cloud properties, without the degenerate scenario. These results are also generally applicable to high-contrast spectroscopy with a coronagraph with a similar wavelength coverage and S/N, and can help design the wavelength bandwidth and the observation plan of exoplanet direct-imaging experiments in the future.

中文翻译：

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用反射光谱对系外行星大气进行多轨道相位和多波段表征

对与太空相距甚远的系外行星进行直接成像将获得它们的反射光谱并测量大气特性。先前的计算表明，轨道相位的变化会产生光谱信号，但该信号是否可用于表征大气尚未显示。我们使用目前最真实的模拟器 Starshade Imaging Simulation Toolkit for Exoplanet Reconnaissance 来模拟对 47 UMa b 行星启用星影的观测，以估计由残余星光、太阳闪光和外星光引起的不确定性。然后，我们使用贝叶斯检索算法 EXOREL^R 来确定对使用罗马或可居住系外行星天文台 (HabEx) 类望远镜观测的大气特性的约束，比较在多个轨道相位或多个波段进行观察的策略。在类似罗马的望远镜上，在 600-800 nm 范围内具有约 20% 的带宽，检索发现了一个简并场景，其气体丰度较低，云层比真相更深或不存在。在不同的轨道相位或 800-1000 nm 的第二个 20% 波段重复观察，积分时间相同，因此信噪比 (S/N) 降低，将有效地消除这种退化的解决方案。使用类似 HabEx 的望远镜进行单次观测将对气体丰度和云特性产生高精度约束，而不会出现退化场景。这些结果通常也适用于具有相似波长覆盖范围和 S/N 的日冕仪的高对比度光谱，