  Lithium abundances in open clusters are a very effective probe of mixing
processes, and their study can help to understand the large depletion of
lithium in the Sun. Due to its age and metallicity, the open cluster M67 is
especially interesting on this regard. Many studies on lithium abundances in
M67 have already been performed, but a homogeneous global analysis of lithium
in stars from subsolar up to the most massive members, was never accomplished
for a large sample based on high-quality spectra. We tested our non-standard
models, which were calibrated using the Sun with observational data. We
collected literature data to follow, for the first time in a homogeneous way,
NLTE lithium abundances of all observed single stars in M67 more massive than
about 0.9 solar masses. Our grid of evolutionary models were computed with
non-standard mixing at metallicity [Fe/H] = 0.01, using the Toulouse-Geneva
evolution code. The analysis is started from the entrance in the ZAMS. Lithium
in M67 is a tight function of mass for stars more massive than the Sun, apart
of a few outliers. A plateau in lithium abundances is observed for turn-off
stars. Both less massive and more massive stars are more depleted than those in
the plateau. There is a significant scatter in lithium abundances for any given
mass lower than M <= 1.1 solar masses. Our models qualitatively reproduce most
of the features described above, although the predicted depletion of lithium is
0.45 dex smaller than observed for masses in the plateau region, i.e. between
1.1 and 1.28 solar masses. Clearly, more work is needed to throughly match the
observations. Despite hints that chromospheric activity and rotation play a
role in lithium depletion, no firm conclusion can be drawn with the presently
available data.
