Based on spectroscopic observations collected at the European Southern Observatory (ESO), within the Observatório Nacional ON/ESO and ON/IAG agreements, under FAPESP project N $^{\circ}$ 1998/10138-8.

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Tables 3-5 are only available in electronic form at http://www.aanda.org

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... Allen

Current address: Centre for Astrophysics Research, STRI and School of Physics, Astronomy and Mathematics, University of Hertfordshire, Hatfield, UK.

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