POLCA: POLarization CAused by drifting grains: Revealing the impact on the observable continuum polarization.

• Applicants: Dr. Mario Flock; Professor Dr. Sebastian Wolf
• Subject Area: Astrophysics and Astronomy
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 544937803

How do planets form? This question is one of the key questions in modern astrophysics and it becomes more pressing with over 5,000 confirmed exoplanetary systems. Advanced global theoretical models and state-of-the-art observations are needed to reveal the detailed physical processes of the gas and dust material in protoplanetary disk, to understand how and where the conditions of planet formation are met. Once interstellar micron-sized grains reach higher densities in the disk they start to grow and settle to the disk midplane. Reaching mm-sizes, these dust pebbles start to have a very dynamic evolution, they radially drift and concentrate in disk regions of high gas pressure. At the same time, their growth process continues, triggered by the enhanced dust density due to dust-gas instabilities like streaming instability. With state-of-the-art polarimetry at submillimeter to radio wavelengths we are now able to not only measure the dust density distribution but also to constrain the underlying physical processes. These mm-sized dust pebbles are not perfect spheres, they usually rotate and they start to spin around the rotation axis once an additional torque is acting on them. Recent studies have demonstrated that such an alignment by a mechanical torque can dominate in protoplanetary disks. In this project, we will develop new global dust and gas hydrodynamical models to investigate the impact of drifting grains on the mechanical alignment processes in proto- planetary disks. At the same time, we will evaluate the potential to trace the impact of mechanical grain alignment on observable quantities. This approach not only provides the basis for verifying this effect but also allows us to uncover the potential of dedicated observations, in particular - but not exclusively - of continuum polarization measurements, to narrow down the mechanism of mechanical grain alignment and thus the underlying physical processes and associated parameters. These goals shall be reached by combining the expertise in the fields of dynamical evolution of dust in protoplanetary disks and the prediction and analysis of corresponding observations, present in the two involved research groups.

• DFG Programme: Research Grants
• Co-Investigator: Stefan Reissl, Ph.D.