It is important for understanding stellar evolution to constrain observationally how overshoot occurs for stellar conditions. Simplified models of the dynamics (eg. Zahn 1991) indicate that overshoot results in a slightly subadiabatic region beyond the convectively unstable layers, followed by an almost discontinuous transition to radiative stratification. Abrupt changes such as this contribute with a characteristic periodic signal to the frequencies ωn,l, of modes of low degree l (Gough 1990). This signature may therefore be detectable for distant stars. Here we show that the signal is sensitive to the “severity” of the overshoot and, of practical importance for the solar case, how it may be extracted from modes of higher degree. Finally we apply our method to solar data.
To analyze the applicability of the method, we consider four stellar models, Z
1 — Z
4, with solar mass, radius (R) and luminosity; of these, Z
2 and Z
4 have overshoot. The bases of the nearly adiabatically stratified region in the models are at radii r
d/R = .729, .713, .713 and .700 respectively.