Astrofysiikka

We study the interstellar medium and the star-formation processes, both in the Milky Way and other galaxies.

The research topics include:

• The physical and chemical properties of interstellar molecular clouds and the initial conditions of star formation. The studies use spectral line and continuum observations at far-infrared and radio wavelengths.
• The properties of interstellar dust grains and their evolution that is linked to the star-formation processes. These are studied using continuum observations of the thermal dust emission (at far-infrared wavelengths) and the light scattering (from optical to mid-infrared wavelengths) caused by the dust grains.
• Development of radiative transfer methods and the use of radiative transfer modelling to interpret line and continuum observations. Star-forming clouds are also modelled using the combination of numerical magneto-hydrodynamical simulations and radiative transfer calculations, to produce synthetic observations that are compared to real observations.
• We also develop methods for the analysis of the spectral line and continuum observations. One of the main goals is numerical efficiency (green computing), which often means the use of graphics processing units (GPUs) in the calculations.

The observations are made with the telescopes of the European Southern Observatory (e.g. the VLT and NTT optical/near-infrared telescopes and the APEX and ALMA radio telescopes) and other ground-based radio telescopes (e.g. Effelsberg, IRAM, JCMT, and TRAO). Data from space-borne instruments also play a central role. These include data from past satellite missions (e.g. the Planck, Herschel, and Spitzer satellites) and the James Webb Space Telescope (JWST).

The main topics of the research

• 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.

• Numerical modelling of stellar convection and magnetic fields in local and global geometries, aiming at understanding 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).