# Impact of angular differential imaging on circumstellar disk images

**Authors:** J. Milli, D. Mouillet, A. M. Lagrange, A. Boccaletti, D. Mawet, G. Chauvin, M. Bonnefoy  
**arXiv:** [1207.5909](https://arxiv.org/abs/1207.5909)  
**Date:** 2012-07-25  
**Summary page:** https://www.summarizepaper.com/en/paper/1207.5909v1/

## Key points

- Direct imaging of circumstellar disks requires high-contrast and high-resolution techniques
- Angular differential imaging (ADI) is a method used for extended objects like circumstellar disks
- Disk images reduced with ADI depend on the amplitude of field rotation and the ADI data reduction strategy, which affect disk observable properties
- A team of researchers aimed to characterize the applicability and biases of some ADI data reduction strategies for different disk morphologies
- The study proposed improvements to classical ADI to limit biases on extended objects by using simulated disks seen under various observing conditions to reduce ADI data and quantify resulting biases
- One key finding was that ADI induces flux losses on disks, making this technique appropriate only for low-to-medium-inclination disks
- Biases alter the disk observable properties such as the slopes of their surface brightness or their radial/azimuthal extent
- This work demonstrated that ADI can easily create artificial features without involving astrophysical processes
- Overall, this study provides important insights into how best to use ADI techniques when studying circumstellar disks while highlighting potential biases and limitations that need to be considered in future research.

## Summary

The direct imaging of circumstellar disks requires high-contrast and high-resolution techniques, with the angular differential imaging (ADI) technique being one such method. Initially developed for point-like sources, ADI is now increasingly applied to extended objects like circumstellar disks. However, this new field of application raises many questions as the disk images reduced with ADI depend strongly on the amplitude of field rotation and the ADI data reduction strategy, both of which directly affect the disk observable properties. To address these issues, a team of researchers aimed to characterize the applicability and biases of some ADI data reduction strategies for different disk morphologies. They placed particular emphasis on parameters mostly used for disks: their surface brightness, their width for a ring, and local features such as gaps or asymmetries. The team first presented a general method for predicting and quantifying those biases before illustrating them for some widely used ADI algorithms applied to typical debris disk morphologies: inclined rings with various inner/outer slopes and width. The study also aimed to propose improvements to classical ADI to limit biases on extended objects by using simulated disks seen under various observing conditions to reduce ADI data and quantify resulting biases. These conclusions complemented previous results from NaCo L' real-disk images of HR4796A. One key finding was that ADI induces flux losses on disks, making this technique appropriate only for low- to medium-inclination disks. A theoretical criterion was derived to predict the amount of flux loss for a given disk morphology, with quantitative estimates of the biases given in some specific configurations. These biases alter the disk observable properties such as the slopes of their surface brightness or their radial/azimuthal extent. Additionally, this work demonstrated that ADI can very easily create artificial features without involving astrophysical processes. Overall, this study provides important insights into how best to use ADI techniques when studying circumstellar disks while highlighting potential biases and limitations that need to be considered in future research.