[1] Max Planck Inst Astron, Konigstuhl 17, D-69117 Heidelberg, Germany
[2] Friedrich Schiller Univ Jena, Inst Solid State Phys, Astrophys Lab, Helmholtzweg 3, D-07743 Jena, Germany
[3] Friedrich Schiller Univ Jena, Inst Solid State Phys, Cluster Phys Grp, Helmholtzweg 3, D-07743 Jena, Germany
[4] Friedrich Schiller Univ Jena, Inst Solid State Phys, Helmholtzweg 3, D-07743 Jena, Germany