On moving shadows and pressure bumps in HD 169142

The search for young planets had its first breakthrough with the detection of the accreting planet PDS70b. To broaden our understanding of planet formation, in particular towards systems such as HR8799 and our Solar System, it is inevitable to study such systems during their formation. Our previous study on HD169142, one of the closest Herbig stars, points towards a shadow-casting protoplanetary candidate (Bertrang+2018). Here, we present follow-up observations to test our previously proposed hypothesis. In order to test for a moving shadow, this data set has to be as comparable as possible to our previous observation. Therefore, we obtain SPHERE/ZIMPOL observations using polarimetric differential imaging (PDI) in the same manner as we did before. We then set our new data into context with previous observations to follow structural changes in the disk over the course of 6 years. The comparison of the structures in HD 169142 over the course of three epochs reveals spatially resolved systematic changes in the position of the previously described surface brightness dip in the inner ring. We further find changes in the brightness structure in azimuthal direction along the ring. And finally, a comparison of our SPHERE/ZIMPOL data with recent ALMA observations reveals a wavelength dependent radial profile of the bright ring. The time-scale on which the changes in the ring's surface brightness occurs suggest that they are caused by a shadow cast by a 1-10Mj planet surrounded by dust. Being located at about 12au from the star, the shadow-casting candidate's orbit is comparable to those of the giant planets in our own Solar System. In addition, we find the first indications for temperature-induced instabilities in the ring. And finally, we trace a pressure maxima, for the first time spatially resolved, with a width of 4.5au. (abbrev.)