Summary The discovery and study of extra solar planets is one of the most exiting research areas in contemporary astrophysics. To understand these alien worlds as well as their formation and evolution it is crucial to measure accurate parameters of the stars they orbit. For stars in the solar neighborhood interferometers - arrays of optical telescopes which combine their light - are well suited. The Carlsberg research infrastructure grant will be used to develop - together with an international team - a new instrument which will be deployed at the CHARA array located at the Mt. Wilson observatory in the USA. This new instrument will improve the capabilities of the CHARA array for the study of extrasolar planet systems and help Danish astronomers to better understand planet formation.