7 Final discussion and conclusion

Far-UV data obtained by FUSE for the pole-on Be star HR 5223 allowed us to determine the column densities of several elements which appear in the ISM. Most of the studied elements are depleted relative to the solar abundance in the same way that they are in other lines of sight.

The presence of the interstellar lines sensitively lowers the global energy distribution in the far-UV (Fig. 6). Once accounting for this effect, neither continuum emission nor line emission, even in the first hydrogen lines of the Lyman series were observed in the FUSE spectra. In particular, in the FUSE wavelength range we found no trace of any spectral characteristic that could be attributed to the circumstellar envelope. As shown by the good agreement we found between observations and theory, the total hydrogen column density enabled us to determine a reliable value of the E(B-V)colour excess towards HR 5223 due only to the ISM.

The column densities of the IS elements observed towards the star clearly show that HR 5223 is located between 250 pc and 900 pc. The distance of the star was determined from a direct comparison of the UV observations to theoretical spectra that accounted for effects of fast rotation.

The characteristics of the O VI resonance lines in the FUSE spectral region and the circumstances of its appearance, together with those of C IV and Si IV resonance lines seen in the IUE spectra, will be discussed in a separate contribution.

Acknowledgements

We would like to thank Drs M. Lemoine, I. Hubeny and T. Lanz for allowing us to use their computer codes. We thank Dr A. Lecavelier des Etangs for his comments and help in using the OWENS computer code. We also wish to thank Dr B.D. Savage, our referee, for useful comments that improved the final version of our paper.

This research has been partially supported by a Marie Curie Fellowship of the European Community programme FP5 under contract number HPMF-CT-2000-00497.

Our work is based on INES data from the IUE and FUSE satellites while bibliographic researches were perform using the SIMBAD and ADS databases.