HOW GOLF SEES THE SECOND HELIUM IONIZATION LAYER ACROSS THE SOLAR CYCLE

摘要

Previous works using intermediate-degree modes [1], but recently also low-degree modes [2] have shown variations with magnetic activity in the adiabatic exponent Γ{sub}1 in the second Helium ionization region. Using ten years of low-l p-mode observations carried out by GOLF instrument (on board SOHO spacecraft), we propose a methodology to isolate the signal from the Hell zone using the second difference δ{sub}(2υ) and the phase shift derivative β{sup}*. Then, we look for possible variations of the parameters which characterize this layer near the solar surface across the solar cycle.