Analyzing the Atmospheric Dispersion Correction of the Gemini Planet Imager: residual dispersion above design requirements

Abstract

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 less than 5 mas of residual DAR to avoid potentially affecting the coronagraph, the GPI ADC averages $\sim 7$ and $\sim 11$ 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 a new approximation for the index of refraction of air from 0.7 microns to 1.36 microns that more accurately accounts for the effects of humidity.

21 pages, 10 figures, published in JATIS

References in corpus (8)

• The Gemini Planet Imager: First Light
• The Gemini Planet Imager Exoplanet Survey: Giant Planet and Brown Dwarf Demographics From 10-100 AU
• Refractive Index of Humid Air in the Infrared: Model Fits
• Astrometry and Photometry with Coronagraphs
• Gemini Planet Imager Observational Calibrations V: Astrometry and Distortion
• Automated data processing architecture for the Gemini Planet Imager Exoplanet Survey
• Quantification of the expected residual dispersion of the MICADO Near-IR imaging instrument
• Characterization of the Atmospheric Dispersion Corrector of the Gemini Planet Imager