Differential rotation of giants and fast-rotating dwarf stars

• Applicant: Professor Dr. Günther Rüdiger
• Subject Area: Astrophysics and Astronomy
• Term: from 2007 to 2011
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 50602300

In recent models of the solar dynamo both differential rotation and meridional flow play important parts. Understanding these phenomena is therefore essential for the theory of stellar activity. A numerical study of the differential rotation of giants and rapidly rotating MS stars by means of a new MHD code for parallel computers is thus proposed.Based on a successful model of the solar rotation (see the coverplot) we have developed a code that predicts the rotation and meridional flow pattern of stellar convection zones. So far our computations have been restricted to solar-type stars of slow and intermediate rotation. Models for these stars always produce solar-type rotation laws with the equator rotating faster than the poles where the equator-pole difference of the rotation rate Q hardly depends on the rotation period. The theory for such stars is supported by recent satellite-based observations of young solar-type stars with about 10 days rotation period.Doppler imaging of HD 31993 finds, however, an anti-solar rotation law for this K2-giant with decelerated equator. The angular momentum conservation law predicts such a pattern in case of very fast meridional flow which is indeed observed. We therefore propose to compute the rotation of HD 31993 and other giant stars. Another class of stars with intense meridional circulation are very young fast-rotating MS stars.As there is also an increasing amount of observations of F-type stars with rotation periods as short as ≈ 1d we plan to apply the model also to these objects with their rather thin convection zones. Such completely new results can only be derived with a code which fulfills highest constraints for resolution and numerical stability.

• DFG Programme: Research Grants
• Participating Person: Dr. Manfred Küker