Searching for Earth-mass Planets Around a Centauri: Obtaining Precise Radial Velocities from Composite Spectra

摘要

For the last five years we have been undertaking an extensive observational campaign that aims to detect terrestrial planets in our neighboring star system a Centauri using the Doppler method. The most challenging problem we have encountered in reducing the observations is the spectral cross-contamination from the other star owing to the small angular separation between the two components of the a Cen AB binary system. In order to overcome this complication we have developed a modified version of a well-established Doppler code that takes the contamination into account by modeling the observations using two stellar templates simultaneously. We present some promising initial results obtained with this new data reduction pipeline and comment on the detectability of Earth-mass planets in the a Centauri system. After correcting for the contamination we achieve a radial velocity precision of typically 2.5 m s~(-1) for a given night of observations, which is a significant improvement of the radial velocity scatter compared to the uncorrected velocities, thus increasing the chances of detecting any potential terrestrial planets. Double-lined spectroscopic binaries present a similar case of composite spectra. Therefore, we have also applied this new Doppler code to several double-lined spectroscopic binary systems and have successfully recovered radial velocities for both components simultaneously.