Stellar magnetic activity

The main topics of the research

1) Photometric, spectroscopic and spectropolarimetric observations of stars at various evolutionary stages, ranging from young main-sequence stars to RS CVn type systems.

  • The main instrument used is the high-resolution echelle spectropolarimeter SOFIN, currently located at Nordica Optical Telescope, La Palma, Spain.
  • Unique spectroscopic time series, extending over 20 years, collected of various late-type stars, the last 8 years in the spectropolarimetric mode.
  • Doppler and Zeeman-Doppler imaging methods used to invert the observational data into surface maps of temperature and magnetic field.
  • Photometric data, with even longer time extent and better time sampling, obtained via international collaboration, and analysed with time series analysis methods developed within the group.

Temperature maps of II Peg constructed using Doppler imaging. Temperature maps of II Peg constructed using Doppler imaging.

2) Numerical modelling of stellar convection and magnetic fields in local and global geometries, aiming at understading the observed magnetic activity ranging from the Sun to our observational targets.

  • The main line of study is the excitation of dynamos in direct simulations of turbulence and convection in Cartesian and spherical geometries and the generation of differential rotation in the Sun and other stars.
  • The simulation results for differential rotation and dynamos are compared with observational data of stars in different evolutionary stages.
  • Mean-field models of differential rotation and dynamos using turbulent transport coefficients from closure models and/or direct simulations.
  • Development of numerical methods suitable for Graphics Processing Units (GPU) within the `Active Suns' research project.
  • The bulk of the computations are made at CSC - IT Center for Science in Espoo, Finland. The group uses roughly 5 million CPU hours yearly.
  • Projects related to the research have been awarded CSC Grand Challenge special allocations in 2008 (DYNAMO08, 1.66M CPU hours), and in 2012 (NEMPI, 2.1M CPU hours)(2), and by Distributed European Infrastructure for Supercomputing Applications (DEISA) in 2008 (CONVDYN, 0.9M CPU hours).

Numerical simulations. Results from numerical convection and dynamo simulations.