5 Conclusions

We have obtained Be abundances for a sample of planet hosts stars, and a smaller sample of stars without known giant planetary companions, aimed at studying the existence of any significant difference between the two groups. Our data also allow us to further investigate Li and Be depletion among metal-rich stars. The objects have metallicities between about -0.6 and +0.5 dex, and cover the temperature interval between $\sim$5150 K and 6450 K. The main conclusions go as follows:

• No particular difference was found between the Be abundances of stars with and without giant planetary companions in the temperature interval for which both groups were observed. This may be interpreted as an argument against the "pollution scenario'' as the source of the high-[Fe/H] observed for planet host stars. However, given the low number of comparison stars available in this study, no strong constraints can still be set.

• For stars with $T_{\rm eff}<5500$ K, the general trend of the Be abundances is not well described by models of light element depletion for solar metallicity (e.g. Pinsonneault et al. 1990). These inconsistencies may be connected either to some metallicity effect, or to some problem with the models, but at the moment we cannot completely discard some relation with the presence of a planet.

• For temperatures lower than 6300 K, no clear correlated Li and Be pattern is seen, contrary to what was found by other authors for hotter dwarfs (Deliyannis et al. 1998; Boesgaard et al. 2001).

• Our data permit to establish approximate temperature limits for the onset of strong Li and Be depletion for the metal-rich stars studied in this work. For stars with $T_{\rm eff}<5900$ K, severe Li burning is seen, while for Be this limit is around 5400 K.

A large survey for Be in planet and non-planet host stars is currently under way, and we expect it to give new insights into this timely and interesting subject.

Acknowledgements

We thank our anonymous referee for the useful and interesting comments and suggestions. We wish to thank the Swiss National Science Foundation (FNSRS) for the continuous support to this project. This research was also partially supported by the Spanish DGES under project PB98-0531-C02-02. Support from Fundação para a Ciência e Tecnologia, Portugal, to N.C.S. in the form of a scholarship is gratefully acknowledged.