  The line profiles of the stars with v sin i below a few km/s can reveal
direct signatures of local velocity fields (e.g. convection) in stellar
atmospheres. This effect is well established in cool main sequence stars, and
has been detected and studied in three A stars. This paper reports observations
of main sequence B, A and F stars with two goals: (1) to identify additional
stars having sufficiently low values of v sin i to search for spectral line
profile signatures of local velocity fields, and (2) to explore how the
signatures of the local velocity fields in the atmosphere depend on stellar
parameters such as effective temperature T_eff and peculiarity type.
  For stars having T_eff below about 10000 K, we always detect local
atmospheric velocity fields indirectly through a non-zero microturbulence
parameter, but not for hotter stars. Among the A and F stars in our sample
having the sharpest lines, direct tracers of atmospheric velocity fields are
found in six new stars. The velocity field signatures identified include
asymmetric excess line wing absorption, deeper in the blue line wing than in
the red; line profiles of strong lines that are poorly fit by computed
profiles; and strong lines that are broader than they should be for the v sin i
values deduced from weak lines. These effects are found in both normal and Am
stars, but seem stronger in Am stars.
  These data still have not been satisfactorily explained by models of
atmospheric convection, including numerical simulations.
