Since a couple of years the detection of extrasolar planets by measuring precision radial velocities is possible and has led to the detection of a number of extrasolar planetary systems. These systems allow for the first time to investigate various formation scenarious of planetary systems by means of observations. However, the detection of planets around young stars is hampered by the influence of stellar activity on the measurement of precise radial velocities. By simulating the variations of stellar absorption line profiles due to star spots a possible correction method was found by employing a momentum analysis of the absorption line profiles. To investigate the feasibility of the proposed method high resolution optical spectra of the active stars xi Bootis A, HD 166435 and iota Horologii have been obtained covering a whole rotation period with good phase coverage. In the case of xi Bootis A and HD 166435 a correlation between individual line profile asymmetry variations was found, which makes a correction of the radial velocities by 30% possible. By contstructing a mean line profile a correction by 50%, close to the level of measurement precision, is demonstrated for the case of HD 166435. This shows the possibility to correct for activity effects on the radial velocity measurements. Also the possibility of detecting planets still embedded in the protoplanetary accretion disk by means of maser radiation is proposed and discussed. The results indicate that if a planets trigger maser emission in the surround disk, the signal would be periodic and correlated with the radial velocity at which the signal is observed. Finally a study of the circumstellar environment of the extrasolar planetary systems Gliese 86 and iota Horologii using high resolution near infrared and submillimeter observing facilities is presented. This study led to the detection of a previously expected but undetected companion in the Gliese 86 system. The presented observations give no clear indication whether the found object is a brown or a white dwarf. The observations of the circumstellar enviroment did not result in the detection of dusty material around this star. A weak emission of carbon monoxide could have been detected indicating the presence of molecular material around this star. However this result needs future confirmation.

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