# 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/fr/paper/2204.08589v3/

## Abstract

The compact mm-wavelength signal in the central cavity of the PDS70 disc, revealed by deep ALMA observations, is aligned with unresolved Halpha emission, and is thought to stem from a circum-planetary disc (CPD) around PDS70c. We revisit the available ALMA data on PDS70c with alternative imaging strategies, and with special attention to uncertainties and to the impact of the so-called "JvM correction", which is thought to improve the dynamic range of restored images. We also propose a procedure for the alignment and joint imaging of multi-epoch visibility data. We find that the JvM correction exaggerates the peak signal-to-noise of the data, by up to a factor of 10. In the case of PDS70, we recover the detection of PDS70c from the July 2019 data, but only at 8sigma. However, its non-detection in Dec. 2017 suggests that PDS70c is variable by at least 42%+-13% over a 1.75yr time-span, so similar to models of the Halpha variability. We also pick up fine structure in the inner disc, such that its peak is offset by ~ 0.04" from the disc centre. The inner disc is variable too, which we tentatively ascribe to Keplerian rotation as well as intrinsic morphological changes.