Iterative Angular Differential Imaging (IADI): An exploration of recovering disk structures in scattered light with an iterative ADI approach

TL;DR

This paper introduces Iterative Angular Differential Imaging (IADI), a novel technique that enhances the recovery of disk structures in scattered light by iteratively processing ADI data, significantly improving flux recovery and phase function accuracy.

Contribution

The paper presents IADI, an iterative approach to ADI that improves disk signal recovery and phase function estimation, addressing limitations of traditional ADI methods.

Findings

IADI can recover up to 75 times more flux than standard ADI.

IADI improves phase function recovery by a factor of 6.4 in Procrustes distance.

Higher signal-to-noise data benefit more from IADI, showing promising results.

Abstract

Distinguishing signal of young gas rich circumstellar disks from stellar signal in near infrared light is a difficult task. Current techniques such as Angular Differential Imaging (ADI) and Polarimetric Differential Imaging (PDI) cope with drawbacks such as self-subtraction. To address these drawbacks we explore Iterative Angular Differential Imaging (IADI) techniques to increase signal throughput in total intensity observations. This work aims to explore the effectiveness of IADI to recover the self-subtracted regions of disks by applying ADI techniques iteratively. To determine the effectiveness of IADI a model of a disk image is made and post-processed with IADI. In addition, masking based on polarimetric images and a signal threshold for feeding back signal are explored. Asymmetries are a very important factor in recovering the disk due to less overlap of the disk in the data set. In some cases, a factor 75 more flux could be recovered with IADI compared to ADI. The Procrustes distance is used to quantify the impact of the algorithm on the scattering phase function. Depending on the level of noise and the ratio between the stellar signal and disk signal, the phase function can be recovered a factor 6.4 in Procrustes distance better than standard ADI. The amplification and smearing of noise over the image due to many iterations did occur and by using binary masks and a dynamic threshold this feedback was mitigated, but it still is a problem in the final pipeline. Lastly observations of protoplanetary disks made with VLT/SPHERE were processed with IADI giving rise to very promising results. While IADI has problems with low signal-to-noise observations due to noise amplification and star reconstruction, higher signal-to-noise observations show promising results with respect to standard ADI.