Gemini Planet Imager Observational Calibrations XIV: Polarimetric Contrasts and New Data Reduction Techniques

TL;DR

This paper discusses new data reduction techniques for the Gemini Planet Imager's polarimetric mode, improving contrast and reducing systematics in exoplanet and circumstellar disk observations.

Contribution

It introduces advanced flux extraction, flat-field division, and instrumental polarization subtraction methods that enhance polarimetric contrast performance.

Findings

Instrumental polarization is wavelength independent within errors.

Improved contrast curves demonstrate enhanced polarimetric sensitivity.

Data reduction techniques reduce systematics and improve detection capabilities.

Abstract

The Gemini Planet Imager (GPI) has been designed for the direct detection and characterization of exoplanets and circumstellar disks. GPI is equipped with a dual channel polarimetry mode designed to take advantage of the inherently polarized light scattered off circumstellar material to further suppress the residual seeing halo left uncorrected by the adaptive optics. We explore how recent advances in data reduction techniques reduce systematics and improve the achievable contrast in polarimetry mode. In particular, we consider different flux extraction techniques when constructing datacubes from raw data, division by a polarized flat-field and a method for subtracting instrumental polarization. Using observations of unpolarized standard stars we find that GPI's instrumental polarization is consistent with being wavelength independent within our errors. In addition, we provide polarimetry contrast curves that demonstrate typical performance throughout the GPIES campaign.