Seismic measurement of the depth of the solar convection zone

The observed frequencies of solar oscillations have been used to determine the depth of the convection zone. The effect of diffusion of helium and heavy elements on this measurement is studied and it is found that the discontinuity in the composition gradient at the base of the CZ due to diffusion gives rise to some systematic errors in this measurement. Taking into account these systematic errors the base of the CZ is estimated to be at a radial distance of (0.713 +/- 0.001) R.. Further, the estimated opacity at the base of the CZ is found to be consistent with that calculated from the OPAL opacity tables using the current value of Z/X. Assuming that the OPAL tables correctly represent the opacity of solar material the surface Z/X is estimated to be 0.0245 +/- 0.0008.