Based on observations made at Observatório do Pico dos Dias/LNA (Brazil).

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Figures 5 to 18 are only available in electronic form at http://www.aanda.org

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Electronic version of the spectra (fichiers FITS) 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/465/993

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