Seismology of the solar envelope: the base of the convective zone as seen in the phase shift of acoustic waves

At the base of the convective zone, discontinuities in the derivatives of the sound speed produce a phase shift in acoustic waves. This phase shift, α0(ν), is inferred by matching the measured solar p-modes to a second-order asymptotic description, the contribution from the surface layers and the second helium ionization zone being subtracted using modes with turning points well inside the convective zone. The resulting phase shift varies quasi-periodically with frequency with a period ≈220 μHz, and has an amplitude ≈8(±4) × 10−4 at a frequency of 3000 μHz. The phase shift α0(ν) is also calculated using the same technique for two solar models, one with no convective penetration and one with penetration extending for 1 per cent of the solar mass. The currently available data are consistent with an overshooting parameter |0≤ε≤0.25|⁠.