1. Department of Physics and Centre for Exoplanets and Habitability, University of Warwick , Gibbet Hill Road, Coventry CV4 7AL, UK
2. Center for Astrophysics, Harvard & Smithsonian , 60 Garden Street, Cambridge, MA 02138-1516, USA
3. Department of Astronomy, University of California, Berkeley , 501 Campbell Hall #3411, Berkeley, CA 94720-3411, USA
4. Institute of Astrophysics, FORTH , GR-71110 Heraklion, Greece
5. Carl Sagan Center, SETI Institute , 189 Bernardo Avenue, Mountain View, CA 94043, USA
6. Department of Physics and Astronomy, University of California , Los Angeles, 430 Portola Plaza, Box 951547, Los Angeles, CA 90095-1547, USA