Figures 4 to 9 are only available in electronic form at http://www.aanda.org

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Table 2 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/469/451

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Figures 4-9 are only available in the electronical edition of the journal.

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