Spectrographs nominally contain a degree of quasistatic optical aberrations resulting from the quality of manufactured component surfaces, imperfect alignment, design residuals, thermal effects, and other other associated phenomena involved in the design and construction process. Aberrations that change over time can mimic the line centroid motion of a Doppler shift, introducing radial velocity (RV) uncertainty that increases time-series variability. Even when instrument drifts are tracked using a precise wavelength calibration source, the barycentric motion of the Earth leads to a wavelength shift of stellar light, which causes a translation of the spectrum across the focal plane array by many pixels. The wavelength shift allows absorption lines to experience different optical propagation paths and aberrations over observing epochs. We use physical optics propagation simulations to study the impact of aberrations on precise Doppler measurements made by diffraction-limited, high-resolution spectrographs. Using the optical model of the iLocater spectrograph, we quantify the uncertainties that cross-correlation techniques introduce in the presence of aberrations and barycentric RV shifts. We find that aberrations that shift the point-spread-function photocenter in the dispersion direction, in particular primary horizontal coma and trefoil, are the most concerning. To maintain aberration-induced RV errors <10 cm / s, phase errors for these particular aberrations must be held well below 0.05 waves at the instrument operating wavelength. Our simulations further show that wavelength calibration only partially compensates for instrumental drifts, owing to a behavioral difference between how cross-correlation techniques handle aberrations between starlight versus calibration light. Identifying subtle physical effects that influence RV errors will help to ensure that diffraction-limited planet-finding spectrographs are able to reach their full scientific potential.

中文翻译：

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研究光学像差对衍射极限径向速度仪器的影响

光谱仪名义上包含一定程度的准静态光学像差，这是由制造组件表面的质量、不完美的对准、设计残留、热效应和其他涉及设计和构造过程的相关现象引起的。随时间变化的像差可以模拟多普勒频移的线质心运动，引入径向速度 (RV) 不确定性，从而增加时间序列可变性。即使使用精确的波长校准源跟踪仪器漂移，地球的重心运动也会导致恒星光的波长偏移，从而导致光谱在焦平面阵列上平移许多像素。波长偏移允许吸收线在观察时期经历不同的光学传播路径和像差。我们使用物理光学传播模拟来研究像差对由衍射受限的高分辨率光谱仪进行的精确多普勒测量的影响。使用 iLocater 光谱仪的光学模型，我们量化了互相关技术在存在像差和重心 RV 偏移时引入的不确定性。我们发现在色散方向上移动点扩散函数光心的像差，特别是初级水平彗形和三叶形，是最令人担忧的。为了保持像差引起的 RV 误差 <10 cm / s，这些特定像差的相位误差必须在仪器工作波长下保持远低于 0.05 波。我们的模拟进一步表明，波长校准只能部分补偿仪器漂移，由于互相关技术如何处理星光与校准光之间的像差的行为差异。识别影响 RV 误差的微妙物理效应将有助于确保衍射极限行星探测光谱仪能够充分发挥其科学潜力。