  The determination of lithium abundances in stars of young clusters have shown
that they deplete Li by different degrees during their pre-main sequence phase.
Beryllium abundances are complementary to the lithium ones, and can help
tracing the mixing processes in the stellar interiors. Our aim is to derive
beryllium abundances in a sample of G- and K-type stars of two young pre-main
sequence open clusters, IC 2391 and IC 2602. The Be abundances are used to
investigate the mixing of internal material in these stars. The reliability of
the Be lines as abundance indicators in low-temperatures is also investigated
in detail. We derived Be abundances from high-resolution, high signal-to-noise
UVES/VLT spectra using spectrum synthesis and model atmospheres. Atmospheric
parameters and other elemental abundances are adopted from a previous work. The
sample stars have masses in the range between 0.80 < M/Msun < 1.20. They have
been shown to differ in lithium abundance by about 0.60 dex, with lower A(Li)
in cooler and lower mass stars. Here, we find that all the stars have the same
Be abundance within the uncertainties. These observations show that the Be
abundance is not affected by the mixing events in the pre-main sequence, in
this mass range, in agreement with the expectation of evolutionary models. A
comparison with Be abundances in older clusters shows that, contrary to the
models, cool stars deplete Be during their main-sequence lifetime, confirming
what has been previously suggested in the literature.
