REXPACO: an algorithm for high contrast reconstruction of the circumstellar environment by angular differential imaging

TL;DR

REXPACO is a new post-processing algorithm that improves high-contrast imaging of circumstellar disks by modeling spatial covariances to reduce artifacts and better preserve disk morphology and photometry.

Contribution

It introduces a novel regularized image reconstruction method based on local covariance learning, enhancing the detection and imaging of circumstellar environments in ADI data.

Findings

Better preservation of disk morphology and photometry compared to standard methods

Reduction of ADI artifacts through spatial covariance modeling

Effective disentangling of circumstellar signals from stellar contamination

Abstract

Aims. The purpose of this paper is to describe a new post-processing algorithm dedicated to the reconstruction of the spatial distribution of light received from off-axis sources, in particular from circumstellar disks. Methods. Built on the recent PACO algorithm dedicated to the detection of point-like sources, the proposed method is based on the local learning of patch covariances capturing the spatial fluctuations of the stellar leakages. From this statistical modeling, we develop a regularized image reconstruction algorithm (REXPACO) following an inverse problem approach based on a forward image formation model of the off-axis sources in the ADI sequences. Results. Injections of fake circumstellar disks in ADI sequences from the VLT/SPHERE-IRDIS instrument show that both the morphology and the photometry of the disks are better preserved by REXPACO compared to standard postprocessing methods like cADI. In particular, the modeling of the spatial covariances proves usefull in reducing typical ADI artifacts and in better disentangling the signal of these sources from the residual stellar contamination. The application to stars hosting circumstellar disks with various morphologies confirms the ability of REXPACO to produce images of the light distribution with reduced artifacts. Finally, we show how REXPACO can be combined with PACO to disentangle the signal of circumstellar disks from the signal of candidate point-like sources. Conclusions. REXPACO is a novel post-processing algorithm producing numerically deblurred images of the circumstellar environment. It exploits the spatial covariances of the stellar leakages and of the noise to efficiently eliminate this nuisance term.