A Spiral arm or a Vortex in the outer disk of PDS-70 ?

Observing dynamical interactions between planets and disks is key to understanding their formation. Two protoplanets have recently been observed within PDS 70's transition disk, along with an extended signal towards the north-west of the star. In this contribution, I will present a temporal analysis of the PDS 70 disk morphology with the aim of assessing whether it could trace a spiral arm caused by the dynamical interaction between the planet PDS 70 c and the disk - or rather be the footprint of a vortex, which can mimic a spiral-arm in an inclined disk. I will show the PDI and ADI images obtained with SPHERE-IRDIS spanning 6 years of observations. We reduced PDI datasets through the IRDAP polarimetric data reduction pipeline (for PDI data) and a novel algorithm that we developed (MUSTARD, for ADI data). I will explain the principle of our inverse-problem based MUSTARD algorithm. I will then show the trace of the potential spiral that we inferred by identifying local radial maxima in azimuthal slices of the disc in each dataset. I will then compare the measured traces with the expected motion of a spiral launched by planet c - i.e. in rigid-body motion. I will show how the traces seem to perfectly align in all datasets, and will finally discuss the implications of our results on the nature of this extended feature.