  We show that, if solar 5 min. oscillations are excited by convection in the
upper layers of the convective envelope, it is impossible to explain the
opposite line asymmetries observed in the velocity and intensity spectra with
assumptions on the dissipations which reduce the problem to a second order one.
The interpretation of that observation requires to solve the full non-adiabatic
problem which is of the fourth or sixth order. We also analyze the causes of
line asymmetries in the frame of the general problem and we show that to locate
the source, it is better to study line asymmetries not too far from line
centers.
