Tables 2a and 2b are also available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html and Figs. 1 through 36 are only available in the online version of the journal at http://www.edpsciences.com

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Affiliated to the Astrophysics Division of the Space Science Department of ESA.

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