FALCO simulations of high-contrast polarimetry with the Nancy Grace Roman Space Telescope Coronagraph Instrument

TL;DR

This paper uses FALCO simulations to analyze the impact of polarization effects on the Roman Space Telescope's coronagraph, demonstrating that polarimetric differential imaging significantly enhances contrast and can accurately recover polarized signals.

Contribution

It provides a detailed simulation-based characterization of polarization aberrations and instrumental polarization effects for the Roman Coronagraph, informing future high-contrast polarimetric observations.

Findings

PDI improves contrast by a factor of six.

Polarimetric contrast limited by instrumental polarization effects.

Polarized sources can be recovered within 2% accuracy.

Abstract

The Coronagraph Instrument of the Nancy Grace Roman Space Telescope (Roman Coronagraph) will be capable of both total intensity and polarization measurements of circumstellar disks. The polarimetric performance is impacted by polarization effects introduced by all mirrors before the Wollaston prisms. In this paper, we aim to characterize these effects for the Roman Coronagraph in bands 1 and 4 using the FALCO and PROPER packages. We simulate the effect of polarization aberrations that impact the polarimetric contrast and the instrumental polarization effects to study the polarimetric accuracy. We include spacecraft rolls, but leave out systematic camera noise. We find that polarimetric differential imaging (PDI) improves the contrast by a factor of six. The PDI contrast of $\sim 8 \times 10^{-11}$ is limited by polarized speckles from instrumental polarization effects and polarization aberrations. By injecting polarized companions with at various contrast levels and demodulating their polarimetric signal, we recover their source Stokes vector within 2%.