Based on observations taken at the Observatoire de Haute Provence (OHP) (France), operated by the French CNRS, and Calar Alto Observatory (Spain), operated by the Max-Planck-Institut für Astronomie (Heidelberg) jointly with the Spanish National Commission for Astronomy.

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Figure 1 is only available in electronic form at
http://www.edpsciences.org

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... NED

This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

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... STSDAS

IRAF is the Image Analysis and Reduction Facility made available to the astronomical community by the National Optical Astronomy Observatories, which are operated by AURA, Inc., under contract with the U.S. National Science Foundation. STSDAS is distributed by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS 5-26555.

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...

17 out of the 24 objects in commun with Koopmann et al. (2001) have H $\alpha$ data already published in Young et al. (1996) and are thus non-independent measurements. In the comparison between our data and those in the literature we did not use the reference Young et al. (1996) for galaxies in common with Koopmann et al. (2001).

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