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[abridged] Previous analyses of lithium abundances in main sequence and redgiant stars have revealed the action of mixing mechanisms other than convectionin stellar interiors. Beryllium abundances in stars with lithium abundancedeterminations can offer valuable complementary information on the nature ofthese mechanisms. Our aim is to derive beryllium abundances along the wholeevolutionary sequence of an open cluster, IC 4651. These Be abundances are usedtogether with previously determined Li abundances, in the same sample stars, toinvestigate the mixing mechanisms in a range of stellar masses and evolutionarystages. New beryllium abundances are determined from high-resolution, highsignal-to-noise UVES spectra using spectrum synthesis and model atmospheres.The careful synthetic modelling of the Be lines region is used to calculatereliable abundances in rapidly rotating stars. The observed behavior of Be andLi is compared to theoretical predictions from stellar models includingrotation-induced mixing, internal gravity waves, atomic diffusion, andthermohaline mixing. Beryllium is detected in all the main sequence andturn-off sample stars, both slow- and fast-rotating stars, including the Li-dipstars, but was not detected in the red giants. Confirming previous results, wefind that the Li dip is also a Be dip, although the depletion of Be is moremodest than that of Li in the corresponding effective temperature range. Forpost-main-sequence stars, the Be dilution starts earlier within the Hertzsprunggap than expected from classical predictions as does the Li dilution. A cleardispersion in the Be abundances is also observed. Theoretical stellar modelsincluding the hydrodynamical transport processes mentioned above are able toreproduce well all the observed features.

Beryllium abundances along the evolutionary sequence of the open cluster IC 4651 - New test for hydrodynamical stellar models