Three-dimensional magnetic field imaging of protoplanetary disks using Zeeman broadening and linear polarization observations
Journal article, 2023

Context. Magnetic fields are predicted to have a crucial impact on the structure, evolution, and chemistry of protoplanetary disks. However, a direct detection of the magnetic field toward these objects has yet to be achieved. Aims. In order to characterize the magnetic fields of protoplanetary disks, we investigate the impact of the Zeeman effect on the (polarized) radiative transfer of emission from paramagnetic molecules excited in protoplanetary disks. Methods. While the effects of the Zeeman effect are commonly studied in the circular polarization of spectral lines, we also performed a comprehensive modeling of the Zeeman-induced broadening of spectral lines and their linear polarization. We developed simplified radiative transfer models adapted to protoplanetary disks, which we compare to full three-dimensional polarized radiative transfer simulations. Results. We find that the radiative transfer of circular polarization is heavily affected by the expected polarity change of the magnetic field between opposite sides of the disk. In contrast, Zeeman broadening and linear polarization are relatively unaffected by this sign change due to their quadratic dependence on the magnetic field. We can match our simplified radiative transfer models to full polarization modeling with high fidelity, which in turn allows us to prescribe straightforward methods to extract magnetic field information from Zeeman broadening and linear polarization observations. Conclusions. We find that Zeeman broadening and linear polarization observations are highly advantageous methods to characterize protoplanetary disk magnetic fields as they are both sensitive probes of the magnetic field and are marginally affected by any sign change of the disk magnetic field. Applying our results to existing circular polarization observations of protoplanetary disk specral lines suggests that the current upper limits on the toroidal magnetic field strengths have to be raised.

Accretion disks


Stars: formation

Magnetic fields


Radiative transfer

Planets and satellites: formation


Boy Lankhaar

Leiden University

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics

Richard Teague

Massachusetts Institute of Technology (MIT)

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 678 A17

A polarized view on stars, planets and life

Swedish Research Council (VR) (2021-00339), 2021-07-01 -- 2024-06-30.

Subject Categories

Aerospace Engineering

Astronomy, Astrophysics and Cosmology



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