Magnetic fields in Herbig Ae/Be stars

Magnetic fields play a key role in the processes leading to the formation of stars and planets. Analytical models and MHD numerical simulations of the evolution of star-forming cores show that the magnetic field is critical for transporting angular momentum during the protostellar phase and sets the conditions for strongly anisotropic accretion. Pre-main-sequence phases, in which central protostars feed from surrounding planet-forming accretion discs, are especially crucial for understanding how worlds like our Solar System are born. About 20 Herbig Ae/Be stars have been reported to have globally organized magnetic fields. Our analysis of their magnetic fields based on observations obtained with HARPSpol at ESO's 3.6m telescope supports the idea that the low detection rate of magnetic fields in these stars can be explained by the weakness of these fields: only a few stars have magnetic fields stronger than 200, and half of the sample possesses magnetic fields of ~100 G, whereas their lower mass T Tauri counterparts possess kG magnetic fields. Studies of the magnetic field structure combined with the determination of the chemical composition of Herbig Ae/Be stars are extremely important because they enable us to improve our insight into how the magnetic fields in these stars are generated and how they interact with their environment, including their impact on the planet formation process and the planet-disk interaction