[1] Eotvos Lorand Univ, Inst Phys & Astron, Pazmany Peter Setany 1-A, H-1117 Budapest, Hungary
[2] Konkoly Observ Budapest, HUN REN CSFK, Konkoly Thege Mut 15-17, H-1121 Budapest, Hungary
[3] Univ Szeged, Dept Expt Phys, Dom ter 9, H-6720 Szeged, Hungary
[4] Univ Texas Ausin, Dept Astron, 2515 Speedway Stop C1400, Austin, TX 78712 USA