1. Université de Strasbourg, CNRS, Observatoire Astronomique de Strasbourg , UMR 7550, F-67000 Strasbourg , France
2. Astronomical Institute, Academy of Sciences of the Czech Republic , Boční II, CZ-14131 Prague , Czech Republic
3. Astronomical Institute, Charles University , V Holešovičkách 2, CZ-18000 Prague , Czech Republic