Solar and Stellar Physics

An understanding of the structure and evolution of stars is central to much of astrophysics. The importance of stellar astrophysics is evident in a broad range of areas. Stars are the 'clocks' with which to measure the age of stellar systems within our Galaxy, providing constraints on the ages of different stellar components and hence on structure, evolution and age of the Galaxy itself. They are used for calibrating age and distance measurements in the Universe on the largest scales. Stars are the sites of most of the chemical evolution in the Universe, elements being created and destroyed by nuclear burning in stellar interiors, and the processed material being subsequently ejected into the interstellar medium. Stars are also laboratories in which to study physical processes of importance both in stellar evolution and in other areas of astrophysics, such as convection, nucleosynthesis, mass loss and accretion, rotation and magnetic fields.

The Sun is uniquely valuable in our study of stars in that we can study it close up, observing many phenomena that surely also take place in other stars but which cannot be resolved because of the enormous distances between those stars and the Earth. The Group has special interests in: helioseismology and asteroseismology - the study of the interior of the Sun and stars using observations of their resonant oscillations; convection inside stars; stellar dynamos; stellar rotation; and more generally astrophysical fluid dynamics inside stars. Members of the group are active participants in various helioseismology and asteroseismology projects. In helioseismology, we use data from the ground based networks BiSoN and GONG, and space data from the MDI, GOLF and Virgo experiments on the ESA/NASA SoHO satellite and the NASASolar Dynamics Observatory. In asteroseismology we have a leadership role in the French/ESA/International satellite CoRoT and contribute to the analysis and application of data from the NASA mission Kepler. We also have an substantial role in the potential future ESA mission PLATO which is one of 3 candiadate for 2 launch slots in 2018. The group has both theoretical and data analysis interests in these convection, rotation and dynamos and magnetic fields as well in astero- and helioseismology.

Highlights

Research activities cover stellar structure and evolution, helio and asteroseismology, rotation, convection, and solar and stellar dynamos.

Roxburgh is ESA Scientist on CoRoT and leads an international co-I group in asteroseismology. Roxburgh and Vorontsov have developed unique seismic inversion techniques to diagnose the internal structure of stars. Roxburgh developed 2-d techniques for modelling rapidly rotating stars and is investigating the effect of rapid rotation on oscillations. With Kupka (Munich) he developed Reynolds stress models of convection to study core overshooting which will be compared with 3-d numerical simulations in progress.

Tavakol and co-workers employed nonlinear dynamo models to successfully account for several important spatio-temporal features in the solar convection zone obtained by recent inversions. He leads an extensive study of the interaction between rotation, convection and magnetic fields in solar-type stars using 3-d simulations in spherical settings.

Vorontsov obtained a very high precision inversion for solar differential rotation using data from MDI which showed the toroidal oscillations predicted by Tavakol. He has developed (with Jeffries, Hawaii) a new high precision inversion technique for helioseismology, fitting the power spectrum directly without the intermediate step of estimating frequencies.