# Variable structure in the PDS70 disc and uncertainties in radio-interferometric image restoration

**Authors:** Simon Casassus, Miguel Carcamo  
**arXiv:** [2204.08589](https://arxiv.org/abs/2204.08589)  
**Date:** 2022-04-18  
**Summary page:** https://www.summarizepaper.com/en/paper/2204.08589v3/

## Key points

- Simon Casassus and Miguel Carcamo study the variable structure of the PDS70 disc and uncertainties in radio-interferometric image restoration.
- They focus on the compact mm-wavelength signal in the central cavity of the PDS70 disc, believed to originate from a circum-planetary disc surrounding PDS70c.
- Researchers reanalyze ALMA data on PDS70c using alternative imaging strategies, paying attention to uncertainties and applying the "JvM correction" technique to enhance dynamic range.
- The JvM correction amplifies peak signal-to-noise ratio by up to a factor of 10, aiding in detecting PDS70c at an 8sigma level in July 2019 data.
- Variability analysis shows that PDS70c was not detected in December 2017, indicating variability of at least 42%+-13% over 1.75 years.
- Inner disc structure examination reveals fine details with peak offset by approximately 0.04" from center, showing variability attributed to Keplerian rotation effects and morphological alterations.
- The study sheds new light on complex dynamics within the PDS70 system and emphasizes accounting for uncertainties in radio-interferometric image restoration techniques.

## Summary

In their study, Simon Casassus and Miguel Carcamo delve into the variable structure of the PDS70 disc and uncertainties in radio-interferometric image restoration. They focus on the compact mm-wavelength signal found in the central cavity of the PDS70 disc, which was initially discovered through deep ALMA observations. This signal is intriguingly aligned with unresolved Halpha emission and is believed to originate from a circum-planetary disc (CPD) surrounding PDS70c. To further investigate this phenomenon, the researchers reanalyze the existing ALMA data on PDS70c using alternative imaging strategies. They pay particular attention to uncertainties in the data and explore the impact of the "JvM correction," a technique designed to enhance the dynamic range of restored images. Additionally, they introduce a novel procedure for aligning and jointly imaging multi-epoch visibility data. One key finding of their study is that the JvM correction tends to amplify the peak signal-to-noise ratio of the data by as much as a factor of 10. Despite this enhancement, when examining the July 2019 data, they only manage to detect PDS70c at an 8sigma level. Interestingly, their analysis reveals that PDS70c was not detected in December 2017, suggesting that it exhibits variability of at least 42%+-13% over a span of 1.75 years—a variability pattern akin to models predicting Halpha variability. Moreover, by scrutinizing the inner disc structure, Casassus and Carcamo observe fine details indicating that its peak is offset by approximately 0.04" from the disc center. They also note variability within this inner disc region, tentatively attributing these changes to both Keplerian rotation effects and intrinsic morphological alterations. Overall, their comprehensive analysis sheds new light on the complex dynamics at play within the PDS70 system and underscores the importance of accounting for uncertainties in radio-interferometric image restoration techniques when studying such intricate astrophysical phenomena.