SIMBAD references

Protoplanetary disks around young stars are the birth-sites of planets. Spectral energy distributions and direct images of a subset of disks known as transition disks reveal dust-depleted inner cavities. Some of these disks show asymmetric structures in thermal submillimetre emission and optical scattered light. These structures can be the result of planet(s) or companions embedded in the disk. We aim to detect and analyse the scattered light of the transition disk J160421.7-213028, identify disk structures, and compare the results with previous observations of this disk at other wavelengths. We obtained and analysed new polarised intensity observations of the transition disk J160421.7-213028 with VLT/SPHERE using the visible light instrument ZIMPOL at R'-band (0.626µm). We probed the disk gap down to a radius of confidence of 0.1'' (∼15AU at 145pc). We interpret the results in the context of dust evolution when planets interact with the parental disk. We observe a gap from 0.1 to 0.3'' (∼15 to 40AU) and a bright annulus as previously detected by HiCIAO H-band observations at 1.65µm. The radial width of the annulus is around 40AU, and its centre is at ∼61AU from the central star. The peak of the reflected light at 0.626µm is located 20AU inward of the cavity detected in the submillimetre. In addition, we detect a dip at a position angle of ∼46.2±5.4°. A dip was also detected with HiCIAO, but located at ∼85°. If the dip observed with HiCIAO is the same, this suggests an average dip rotation of ∼12°/year, which is inconsistent with the local Keplerian angular velocity of ∼0.8°/yr at ∼61AU. The spatial discrepancy in the radial emission in J160421.7-213028 at different wavelengths is consistent with dust filtration at the outer edge of a gap carved by a massive planet. The dip rotation can be interpreted as fast variability of the inner disk and/or the presence of a warp or circumplanetary material of a planet at ∼9.6AU.