THERMAL AND MECHANICAL DAMPING OF SOLAR P-MODES

Nonadiabatic effects associated with the transfer of energy and with turbulent stresses add small imaginary parts, omega-i(1) and omega-i(2), to solar p-mode eigenfrequencies. Numerical calculations have shown that these quite different processes make comparable contributions to omega-i at frequencies well below the acoustic cutoff at omega-ac. We derive analytic expressions which reveal the connection between omega-i(1) and omega-i(2). Our estimates yield omega-i proportional omega-8 for omega << omega-ac, in good agreement with the numerical calculations. However, the observed line width is proportional to omega-4.2 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 omega-i at omega << omega-ac.