On the detection of pure sine waves embedded in a spectrum of stochastically excited p modes

Abstract

The mode identification and fitting of solar oscillations provide an observational tool to derive the physical properties of the Sun’s interior. What has been devised for helioseismology can now be used for future asteroseismology ground-based instruments and space missions, such as the High-Accuracy Radial Velocity Planetary Searcher (HARPS) and Convection, Rotation and Planetary Transits (COROT). In the coming decade, numerous stars will be observed for which new tools will be needed. For instance, it is very likely that g and p modes will be detected, rendering the identification difficult. In addition, modes having both characteristics, known as mixed modes, are also likely to be detected in evolved stars; these latter modes are crucial for the understanding of the internal structure of the stars as they propagate deeply inside the stars, unlike the p modes. Unfortunately, the mixing will not only occur physically but also in the frequency domain: mixed modes will appear very close to stochastically excited p modes. In this paper, we have devised a new technique for detecting long-lived modes (mixed or g modes) embedded in a common p-mode spectrum. The technique has been validated using Monte Carlo simulations. In the framework of the hare-and-hound exercise of COROT, this technique has been applied to synthetic time series of the evolved solar-like star HD 57006. The results show that we can detect most of the mixed modes embedded by the hare. We also discuss the impact of how the long-lived modes are excited on the detection level. The technique described here can be applied to stars with a mass greater than 1.2 M� ,h a ving evolved possibly beyond the terminal-age main sequence, such as Procyon. Ke yw ords: methods: statistical ‐ stars: oscillations.