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K. Huber

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Research: Planets around active stars

The deformations of line profiles in spectra can tell a lot about the activity and surface structure of a star. These variations of the line's shape can be used to create Doppler Images, which show the spot distribution on the star's surface, if appropriate data and necessary information about the star (for example its exact rotation period) are available. Additionally the rotation velocity of stars one wants to use for Doppler Imaging has to be higher than approximately 25 km/s.
By nature radial velocity measurements of such fast rotating stars are especially difficult, because the error increases with the width of the line. Considering stellar activity, which causes asymmetric line profile deformations, it is even more problematic to get RV measurements with accuracies of a hundred m/s or less, which must be achieved for planet detections.
To increase the accuracy of RV measurements of heavily Doppler broadened spectra, the influences of stellar activity on the line profiles must be analyzed in detail. This enables us to distinguish between RV shifts due to line profile deformation and RV shifts due to stellar companions such as planets.

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