The radial velocity of the sun as a star and the solar cycle

Radial velocity measurements of the sun as a star using a resonant scattering spectrometer have been obtained at Izaña (Tenerife) during long observing seasons from 1976 to 1985. Its analysis shows that except for the global oscillations with periods shorter than one day there are stable signals with longer periods: at ∼13 days with mean amplitude of ∼ 3 m/s (it changes with the solar cycle) and another one of ∼ 15 m/s amplitude which shows a temporal variation of various years related to the solar cycle. The first signal has a partial explanation as an effect produced by the passage of active regions through the visible surface of the sun but it does not completely explain the observed signal. The second one, related to the limb shift, is probably due to changes in the convection zone in connection with the solar cycle.