1. Department of Physics and Astronomy, University College London , Gower Street, WC1E 6BT London , United Kingdom
2. Tartu Observatory , Observatooriumi 1, Tõravere 61602, Tartu , Estonia
3. Laboratory for Astrophysics, Leiden Observatory, Leiden University , P.O. Box 9513, NL-2300 RA Leiden , the Netherlands
4. Department of Astronomy, University of Virginia , Charlottesville, VA 22904 , USA
5. Center for Space and Habitability, Universität Bern , Gesellschaftsstrasse 6, CH-3012 Bern , Switzerland
6. National Astronomical Observatory of Japan , Osawa 2-21-1, Mitaka, Tokyo 181-8588 , Japan
7. Department of Earth Sciences & Institute of Astronomy, University of Cambridge, CB3 OHA. , United Kingdom