Multi-wavelength study of the HD 163296 disk: measuring local variations of dust properties

Greta Guidi, Andrea Isella, Leonardo Testi, Claire Chandler, Hau-Yu Baobab Liu, Hans Martin Schmid, Giovanni Rosotti, Cody Meng, Jeff Jennings, Jonathan Williams, John Carpenter, Itziar deGregorio-Monsalvo, Hui Li, Shangfei Liu, Sergio Ortolani, Sascha Quanz, Luca Ricci, Marco Tazzari

The Atacama Large Millimeter/submillimeter Array (ALMA) provided in the last years observations of protoplanetary disks at unprecedented resolution and sensitivity. The plethora of images revealing small-scale structures in the dust and gas distribution of several targets raised many questions about the mechanisms responsible of perturbing the disks. The derivation of the underlying properties of the emitting material is nontrivial because of the complex radiative processes involved.

The bright ringed disk around the Herbig star HD 163296 has been the subject of several studies, aiming at constraining dust and gas properties and finding evidence of protoplanets. We combined observations of HD 163296 from ALMA and the Very Large Array (VLA) at a high angular resolution corresponding to 5 ? 8 au, to determine the dust spatial distribution and grain properties across the disk. We show that the assumptions on the dust composition have a strong impact on the derived surface densities and grain size. In particular, increasing the porosity of the grains to 80% results in a total dust mass about five times higher with respect to grains with 25% porosity. Finally, we find that the derived opacities as a function of frequency deviate from a simple power law and that grains with a lower porosity seem to better reproduce the observations. While we do not find evidence of differential trapping in the rings of HD 163296, our overall results are consistent with the postulated presence of giant planets affecting the dust temperature structure and surface density, and possibly originating a second-generation dust population of small grains.

<a href=";A...664A.137G/doi:10.1051/0004-6361/202142303">10.1051/0004-6361/202142303</a>