One of the top priorities in observational astronomy is the direct imaging and characterization of extrasolar planets (exoplanets) and planetary systems. Direct images of rocky exoplanets are of particular interest in the search for life beyond the Earth, but they tend to be rather challenging targets since they are orders-of-magnitude dimmer than their host stars and are separated by small angular distances that are comparable to the classical $\lambda /D$ diffraction limit, even for the coming generation of 30 m class telescopes. Current and planned efforts for ground-based direct imaging of exoplanets combine high-order adaptive optics (AO) with a stellar coronagraph observing at wavelengths ranging from the visible to the mid-IR. The primary barrier to achieving high contrast with current direct imaging methods is quasi-static speckles, caused largely by non-common path aberrations (NCPAs) in the coronagraph optical train. Recent work has demonstrated that millisecond imaging, which effectively “freezes” the atmosphere’s turbulent phase screens, should allow the wavefront sensor (WFS) telemetry to be used as a probe of the optical system to measure NCPAs. Starting with a realistic model of a telescope with an AO system and a stellar coronagraph, this paper provides simulations of several closely related regression models that take advantage of millisecond telemetry from the WFS and coronagraph’s science camera. The simplest regression model, called the naïve estimator, does not treat the noise and other sources of information loss in the WFS. Despite its flaws, in one of the simulations presented herein, the naïve estimator provides a useful estimate of an NCPA of ${\sim}0.5$ radian RMS ($\approx \lambda /13$), with an accuracy of ${\sim}0.06$ radian RMS in 1 min of simulated sky time on a magnitude 8 star. The bias-corrected estimator generalizes the regression model to account for the noise and information loss in the WFS. A simulation of the bias-corrected estimator with 4 min of sky time included an NCPA of ${\sim}0.05$ radian RMS ($\approx \lambda /130$) and an extended exoplanet scene. The joint regression of the bias-corrected estimator simultaneously achieved an NCPA estimate with an accuracy of ${\sim}5 \times {10^{- 3}}$ radian RMS and an estimate of the exoplanet scene that was free of the self-subtraction artifacts typically associated with differential imaging. The $5 \sigma$ contrast achieved by imaging of the exoplanet scene was ${\sim}1.7 \times {10^{- 4}}$ at a distance of $3\lambda /D$ from the star and ${\sim}2.1 \times {10^{- 5}}$ at $10 \lambda /D$. These contrast values are comparable to the very best on-sky results obtained from multi-wavelength observations that employ both angular differential imaging (ADI) and spectral differential imaging (SDI). This comparable performance is despite the fact that our simulations are quasi-monochromatic, which makes SDI impossible, nor do they have diurnal field rotation, which makes ADI impossible. The error covariance matrix of the joint regression shows substantial correlations in the exoplanet and NCPA estimation errors, indicating that exoplanet intensity and NCPA need to be estimated self-consistently to achieve high contrast.

中文翻译：

---

毫秒系外行星成像：一、方法与模拟结果

观测天文学的首要任务之一是太阳系外行星（系外行星）和行星系统的直接成像和表征。岩石系外行星的直接图像在寻找地球以外的生命时特别感兴趣，但它们往往是相当具有挑战性的目标，因为它们比它们的主星暗淡几个数量级，并且被相隔的小角距离与经典的$\lambda /D$衍射极限，即使对于下一代 30 m 级望远镜也是如此。目前和计划中的系外行星地面直接成像工作将高阶自适应光学 (AO) 与恒星日冕仪相结合，观测波长范围从可见光到中红外波段。使用当前直接成像方法实现高对比度的主要障碍是准静态散斑，主要由日冕仪光学系统中的非公共路径像差 (NCPA) 引起。最近的工作表明，毫秒成像可以有效地“冻结”大气的湍流相位屏幕，应该允许波前传感器 (WFS) 遥测技术用作光学系统的探针来测量 NCPA。从带有 AO 系统和恒星日冕仪的现实望远镜模型开始，本文提供了几个密切相关的回归模型的模拟，这些模型利用了 WFS 和日冕仪科学相机的毫秒遥测数据。最简单的回归模型称为朴素估计器，它不处理 WFS 中的噪声和其他信息丢失源。尽管存在缺陷，但在此处介绍的其中一个模拟中，朴素估计器提供了对 NCPA 的有用估计${\sim}0.5$弧度 RMS ( $\approx \lambda /13$ )，在 8 等星的模拟天空时间的 1 分钟内精度为${\sim}0.06$弧度 RMS。该偏差校正估计概括了回归模型占世界粮食首脑会议的噪声和信息丢失。具有 4 分钟天空时间的偏差校正估计器的模拟包括${\sim}0.05$弧度 RMS ( $\approx\lambda /130$ )的 NCPA和扩展的系外行星场景。偏差校正估计器的联合回归同时实现了 NCPA 估计，精度为${\sim}5 \times {10^{- 3}}$弧度 RMS 和对系外行星场景的估计，该场景没有通常与差分成像相关的自减伪影。通过对系外行星场景成像实现的$5\sigma$对比度为${\sim}1.7\times {10^{-4}}$，距离恒星$3\lambda /D$和${\sim} 2.1 \倍{10 ^ { - 5}} $在$ 10 \拉姆达/ d $. 这些对比度值可与从采用角差分成像 (ADI) 和光谱差分成像 (SDI) 的多波长观测中获得的最佳天空结果相媲美。尽管我们的模拟是准单色的，这使得 SDI 不可能，但它们也没有昼夜场旋转，这使得 ADI 不可能，但这种可比的性能仍然存在。联合回归的误差协方差矩阵显示了系外行星和 NCPA 估计误差的显着相关性，表明需要自洽地估计系外行星强度和 NCPA 以实现高对比度。