Projekt F

Doppler Imaging of Stellar Surfaces

Prof. Dr. Klaus G. Strassmeier (AIP, advisor) and Dr. Michael Weber (AIP, co-advisor)

Background: Doppler imaging is an inversion technique, similar to computed tomography (CT) in medicine, which recovers a 2-D image of a rapidly rotating star from a 1-D series of high-resolution spectral line profiles [23]. The inverse problem for stars with cool spots amounts to solving the integral equation relating the surface temperature distribution to the observed line profiles and light and colour curve variations, while controlling the effects of noise in the data through a regularizing functional.

Aims: The scientific goals of the project are to determine differential surface rotation and possibly meridional flow patterns that can be directly compared to flux-tube simulations based on (mean-field) dynamo models. Thanks to our robotic telescope STELLA on Tenerife [24], we have access to targets that could otherwise not be observed properly, e.g., due to solar-like rotation periods of a month and the need for real-time phase sampling. The technical goals of the project are to obtain such a data set and to determine a well-constrained Doppler image from them, or even a series of images, i.e., a movie.

Methods: Our group has developed two inversion codes over the years, TempMap [25] and iMAP [26], that we propose to apply to a unique time-series of high-resolution stellar spectra obtained with our robotic telescope STELLA [24]. Flux-tube simulations based on (mean-field) dynamo models are already at hand at AIP [27] but need to be adapted to the actual target properties. Target properties are planned to be computed with our own node of the MESA stellar structure and evolution code [28]. Finally, the doctoral student shall place the results in context with the semi-empiric predictions of angular momentum in solar-like stars as we know it from open cluster stars.