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Abstract

The aim of my PhD dissertation is the detection and characterization of extrasolar planets around evolved intermediate stars using precise Doppler spectroscopy. I worked with a sample of G and K giants, which have been observed since 1999 at Lick Observatory. Finding planets around evolved stars, however, is an ambitious task. Giants can exhibit intrinsic long-period RV variations that can effectively mimic a planet, such as large surface spots or even non-radial g−mode pulsations. Given the fact that Hamilton spectra have relatively low resolution (R = 60 000) for line profile analysis, those phenomena cannot be excluded. My research focuses on proving the planetary hypothesis for those objects in our science sample that show well-defined RV signature consistent with one or more sub-stellar companion(s). Thus, I have applied two quantitative tests that can finally close the case for our planetary candidates: First, I have developed a data reduction pipeline for the ESO near infrared spectrograph CRIRES (R = 100 000). I have obtained precise RV from the near-IR, and I searched for consistency with the Lick optical data. Intrinsic stellar RV variations will lead to differences in RV phase and amplitude between the optical and near-IR, while, in case of a planet, both data sets are expected to be consistent. Second, I have constructed detailed χ2red grids in order to explore the dynamical properties of the fits around the best fit. Each orbital configuration from the χ2red grids have been tested with the Mercury N-body simulator. Both methods turned out to be very successful and are included as separate parts of my PhD thesis. The near-IR velocity precision is in the order of 30−40 m s−1 , enough to confirm the RV phase and amplitude, and thus, the planetary nature of most of our candidates. The dynamical fitting shows better χ2red values than the multiple Keplerian model. This is a prove that indeed interacting planets are responsible for the Doppler shift. The long term stability test shows that some systems have a stable best fit, while the rest have broad and confident long term-stable regions in orbital parameter space within 1 or 2σ from the best fit.