Temporal and chromatic variation of polarized scattered light in the outer disk of PDS 70

Abstract

PDS 70 is a unique system as it hosts a protoplanetary disk with two confirmed forming planets, making it an ideal target for characterizing dust in such disks. We present new high-contrast polarimetric differential imaging of PDS 70 using the $N\_R$ filter on SPHERE/ZIMPOL, combined with archival VLT/SPHERE data across five wavelengths ($N\_R$, $VBB$, $J$, $H$, and $Ks$) spanning seven epochs over eight years. For each epoch, we corrected smearing effects from instrument resolution, analyzed azimuthal brightness profiles, and derived intrinsic disk-integrated polarized reflectivity and brightness contrasts. Our analysis reveals significant temporal variability in both integrated polarized reflectivity and azimuthal brightness profiles, suggesting variable shadowing on the outer disk from unresolved inner disk structures. Nonetheless, we observe a systematic wavelength-dependent contrast between the near and far sides of the inclined disk, highlighting the need to consider shadowing from the inner disk and surface geometry of the reflecting disk in data interpretation.