Detection of periodic signatures in the solar power spectrum on the track of l=1 gravity modes

Departement Cassiop´ ´ee, UMR CNRS 6202, Observatoire de la C ote d’Azur, BP 4229, 06304 Nice Cedex 4, FranceˆABSTRACTIn the present work we show robust indications of the ex-istence of g modes in the Sun using 10 years of GOLFdata. The present analysis is based on the exploitation ofthe collective properties of the predicted low-frequency(25 to 140 µHz) g modes: their asymptotic nature, whichimplies a quasi equidistant separation of their periods fora given angular degree (l). The Power Spectrum (PS) ofthe Power Spectrum Density (PSD), reveals a significantstructure indicatingthe presenceof features (peaks)in thePSD with near equidistant periods corresponding to l=1modes in the range n=-4 to n=-26. The study of its sta-tistical significance of this feature was fully undertakenand complemented with Monte Carlo simulations. Thisstructure has a confidence level better than 99.86 % notto be due to pure noise. Furthermore, a detailed studyof this structure suggests that the gravity modes have amuch more complex structure than the one initially ex-pected (line-widths, magnetic splittings...). Compared tothe latest solar models, the obtained results tend to fa-vor a solar core rotating significantly faster than the restof the radiative zone. In the framework of the Phoebusgroup, we have also applied the same methodology toother helioseismology instruments on board SoHO andground based networks.Key words: Sun: Helioseismology, Sun: Interior, Sun:Oscillations.1. INTRODUCTIONDetailed knowledge of the solar interior has been ob-tained by means of precise measurements of its acous-tic (p) eigenmodes and the subsequent structural inver-sions, providing the stratification of crucial variables li kethe sound speed down to 0.05 R