Seismic extraction of the convective extent in solar-like stars -: The observational point of view

Convection is the first manifestation of macroscopic motions in stars. In the next decade, the extent of the external convective zone of solar-like stars will have to be derived from the eigenfrequencies of their low-degree (l = 0, 1 and 2) acoustic modes. In this paper, we compare different tracers of the base of the convective zone (BCZ) and show that the second difference delta(2)v stays simple and well suited for analyzing real data. We suggest the use of (t) over tilde (BCZ) = (2(Deltav))(-1) - (tau) over tilde (BCZ) as a quasi-non-biased indicator of the BCZ acoustic radius. The method is first checked on a long-time solar observation with GOLF, then on shorter real observations by VIRGO and 10 000 simulated observations of solar-like stars. We present results for different observational duration and stellar masses. The intrinsic error due to the method on the convective extent is smaller than 1.5% (in units of stellar acoustic radius) for stars with masses between 0.9 and 1.3 M-circle dot. The limited observational interval adds a supplementary uncertainty of about 1.6% for a 150-day long simulated observation. In this study, we have also analyzed the effects of stochastic excitation and of non-continuous runs of shorter lengths. We discuss how to take into account the variations in activity.