This work is part of an ongoing project which aims to detect terrestrial planets in our neighbouring star system \alpha Centauri using the Doppler method .
Owing to the small angular separation between the two components of the \alpha Cen AB binary system , the observations will to some extent be contaminated with light coming from the other star .

We are accurately determining the amount of contamination for every observation by measuring the relative strengths of the H- \alpha and NaD lines .
Furthermore , we have developed a modified version of a well established Doppler code that is modelling the observations using two stellar templates simultaneously .
With this method we can significantly reduce the scatter of the radial velocity measurements due to spectral cross-contamination and hence increase our chances of detecting the tiny signature caused by potential Earth-mass planets .
After correcting for the contamination we achieve radial velocity precision of \sim 2.5 \mathrm { m s ^ { -1 } } for a given night of observations .

We have also applied this new Doppler code to four southern double-lined spectroscopic binary systems ( HR159 , HR913 , HR7578 , HD181958 ) and have successfully recovered radial velocities for both components simultaneously .