The atmospheric dispersion corrector (ADC) of the Gemini Planet Imager (GPI) corrects the chromatic dispersion caused by differential atmospheric refraction (DAR), making it an important optic for exoplanet observation. Despite requiring <5 mas of residual DAR to avoid potentially affecting the coronagraph, the GPI ADC averages ∼7 and ∼11 mas of residual DAR in H and J band, respectively. We analyzed GPI data in those bands to find explanations for the underperformance. We found the model GPI uses to predict DAR underestimates humidity’s impact on incident DAR, causing on average a 0.54 mas increase in H band residual DAR. Additionally, the GPI ADC consistently undercorrects in H band by about 7 mas, causing almost all the H band residual DAR. J band does not have such an offset. Perpendicular dispersion induced by the GPI ADC, potentially from a misalignment in the prisms’ relative orientation, causes 86% of the residual DAR in J band. Correcting these issues could reduce residual DAR, thereby improving exoplanet detection. We also made an approximation for the index of refraction of air from 0.7 to 1.36 microns that more accurately accounts for the effects of humidity.

中文翻译：

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双子座行星成像仪大气色散校正分析：残余色散高于设计要求

双子座行星成像仪（GPI）的大气色散校正器（ADC）可校正由差分大气折射（DAR）引起的色散，使其成为系外行星观测的重要光学器件。尽管需要 <5 mas 的残余 DAR 以避免潜在影响日冕仪，但 GPI ADC 在 H 和 J 波段中平均残余 DAR 分别为 ∼7 mas 和 ∼11 mas。我们分析了这些频段的 GPI 数据，以找出表现不佳的原因。我们发现用于预测 DAR 的 GPI 模型低估了湿度对入射 DAR 的影响，导致 H 波段残余 DAR 平均增加 0.54 mas。此外，GPI ADC 在 H 波段始终存在约 7 mas 的欠校正，导致几乎所有 H 波段残留 DAR。 J波段没有这样的偏移。 GPI ADC 引起的垂直色散（可能是由于棱镜相对方向的未对准）导致 J 波段中 86% 的残余 DAR。纠正这些问题可以减少残留 DAR，从而改善系外行星探测。我们还对 0.7 至 1.36 微米的空气折射率进行了近似，以更准确地解释湿度的影响。