THERMAL AND MECHANICAL DAMPING OF SOLAR p-MODES

Nonadiabatic effects associated with the transfer of energy and with turbulent stresses add small imaginary parts, wji> and w~2>, to solar p-mode eigenfrequencies. Numerical calculations have shown that these quite different processes make comparable contributions to W; at frequencies well below the acoustic cutoff at wac· We derive analytic expressions which reveal the connection between w~ 1 l and w~2>. Our estimates yield W; oc w8 for w ~ wac• in good agreement with the numerical calculations. However, the observed line width is proportional to w4·2 at low frequencies. We suspect that there is an unmodeled component of perturbed convective energy transport or of turbulent viscosity that makes an important contribution to W; at w ~ wac· Subject headings: radiative transfer Sun: oscillations turbulence