Magnetic fields of low-mass pre-main-sequence stars and Brown Dwarfs

• Applicants: Professor Dr. Ralph Neuhäuser; Professor Dr. Ansgar Reiners
• Subject Area: Astrophysics and Astronomy
• Term: from 2009 to 2013
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 105369318

We propose to study magnetic fields in fully convective objects, both weak-line T Tauri stars and (young) Brown Dwarfs. In particular, we will observe the transition from the (/(-dynamo to another turbulent type of dynamo in M-type T Tauri stars (part 1) and in late-M and early-L type Brown Dwarfs (part 2), where we aim to directly measure magnetic fields for the first time. On the main-sequence, the transition from partly radiative to fully convective stars appears at spectral types around M4, but no break in activity nor the mean magnetic field was found here. On the contrary, the fraction of active stars is rising towards cooler stars before it eventually diminishes close to the boundary to Brown Dwarfs. Our strategy is to search for a transition between different types of dynamos by investigating fully convective objects and compare them to the well studied hotter partial radiative stars.In the first part of this project, we measure magnetic fields in young low-mass pre-MS stars by studying Zeeman broadening in magnetically sensitive atomic and molecular lines using established methods. In the second part, the quest for magnetic fields in Brown Dwarfs, we have to develop new strategies to detect Zeeman splitting. We will use high-resolution spectrographs like UVES and CRIRES at the VLT.

• DFG Programme: Research Grants