Gemini Planet imager Observational Calibrations X: Non-Redundant Masking on GPI

TL;DR

This paper discusses the implementation and performance of non-redundant masking on the Gemini Planet Imager, highlighting its calibration, stability, and potential for high-resolution imaging of exoplanets and binary systems.

Contribution

It presents the first on-sky results of NRM on GPI, evaluating its calibration, stability, and imaging capabilities for high-contrast observations.

Findings

NRM provides reliable plate scale calibration.

On-sky data shows stable wavefront error performance.

Successfully resolved a known binary star.

Abstract

The Gemini Planet Imager (GPI) Extreme Adaptive Optics Coronograph contains an interferometric mode: a 10-hole non-redundant mask (NRM) in its pupil wheel. GPI operates at $Y, J, H$, and $K$ bands, using an integral field unit spectrograph (IFS) to obtain spectral data at every image pixel. NRM on GPI is capable of imaging with a half resolution element inner working angle at moderate contrast, probing the region behind the coronagraphic spot. The fine features of the NRM PSF can provide a reliable check on the plate scale, while also acting as an attenuator for spectral standard calibrators that would otherwise saturate the full pupil. NRM commissioning data provides details about wavefront error in the optics as well as operations of adaptive optics control without pointing control from the calibration system. We compare lab and on-sky results to evaluate systematic instrument properties and examine the stability data in consecutive exposures. We discuss early on-sky performance, comparing images from integration and tests with the first on-sky images, and demonstrate resolving a known binary. We discuss the status of NRM and implications for future science with this mode.