[1] Leiden Univ, Leiden Observ, Leiden, Netherlands
[2] Inst Theoret Astrophys, Zentrum Astron, Heidelberg, Germany
[3] Univ Oslo, Inst Theoret Astrophys, Oslo, Norway
[4] Univ Bonn, Argelander Inst Astron, Bonn, Germany
[5] Aix Marseille Univ, CNRS, Lab Astrophys Marseille, Marseille, France
[6] INAF, Osservatorio Astron Bologna, Bologna, Italy
[7] Ist Nazl Fis Nucl, Sez Bologna, I-40126 Bologna, Italy