Seismic extraction of the convective extent in solar-like stars*
The observational point of view
Service d'Astrophysique, CEA/DSM/DAPNIA, CE Saclay, 91191 Gif-sur-Yvette Cedex, France e-mail: [jballot;cturck;rgarcia]@cea.fr
Accepted: 29 April 2004
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 ( 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 stays simple and well suited for analyzing real data. We suggest the use of 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 (in units of stellar acoustic radius) for stars with masses between 0.9 and 1.3. The limited observational interval adds a supplementary uncertainty of about 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.
Key words: convection / stars: oscillations / stars: interiors / Sun: helioseismology / methods: data analysis
© ESO, 2004