Data Reduction Techniques for High Contrast Imaging Polarimetry. Applications to ExPo

TL;DR

This paper discusses data reduction techniques for high contrast imaging polarimetry, demonstrating how to effectively analyze ExPo data to detect circumstellar environments and exoplanets.

Contribution

It introduces specific data reduction steps and analysis methods for dual-beam imaging polarimeters like ExPo, enhancing contrast ratio capabilities.

Findings

Instrumental artifacts can be minimized using fast modulation and dual-beam techniques.

Proper data processing and image alignment are crucial for high contrast imaging.

Imaging polarimetry can resolve circumstellar environments without coronagraphs or adaptive optics.

Abstract

Imaging polarimetry is a powerful tool for detecting and characterizing exoplanets and circumstellar environments. Polarimetry allows a separation of the light coming from an unpolarized source such as a star and the polarized source such as a planet or a protoplanetary disk. Future facilities like SPHERE at the VLT or EPICS at the E-ELT will incorporate imaging polarimetry to detect exoplanets. The Extreme Polarimeter (ExPo) is a dual-beam imaging polarimeter that currently can reach contrast ratios of 10^5, enough to characterize circumstellar environments. We present the data reduction steps for a dual-beam imaging polarimeter that can reach contrast ratios of 10^5. The data obtained with ExPo at the William Herschel Telescope (WHT) are analyzed. Instrumental artifacts and noise sources are discussed for an unpolarized star and for a protoplanetary disk (AB Aurigae). The combination of fast modulation and dual-beam techniques allow us to minimize instrumental artifacts. A proper data processing and alignment of the images is fundamental when dealing with large contrasts. Imaging polarimetry proves to be a powerful method to resolve circumstellar environments even without a coronagraph mask or an Adaptive Optics system.