  Element diffusion is expected to occur in all kinds of stars : according to
the relative effect of gravitation and radiative acceleration, they can fall or
be pushed up in the atmospheres. Helium sinks in all cases, thereby creating a
gradient at the bottom of the convective zones. This can have important
consequences for the sound velocity, as has been proved in the sun with
helioseismology.
  We investigate signatures of helium diffusion in late F-type stars by
asteroseismology.
  Stellar models were computed with different physical inputs (with or without
element diffusion) and iterated in order to fit close-by evolutionary tracks
for each mass. The theoretical oscillation frequencies were computed and
compared for pairs of models along the tracks. Various asteroseismic tests
(large separations, small separations, second differences) were used and
studied for the comparisons.
  The results show that element diffusion leads to changes in the frequencies
for masses larger than 1.2 Msun. In particular the helium gradient below the
convective zone should be detectable through the second differences.
