1. Centro de Astrofísica da Universidade do Porto; Rua das Estrelas; 4150-762; Porto; Portugal
2. Institut de Recherche en Communication et Cybernétique de Nantes; 1 rue de la Noë, BP 92101; 44321; Nantes Cedex 3; France
3. Stellar Astrophysics Centre, Department of Physics and Astronomy; Aarhus University; Ny Munkegade 120; DK-8000; Aarhus C; Denmark