FIRST RESULTS FROM VIRGO, THE EXPERIMENT FOR HELIOSEISMOLOGY AND SOLAR IRRADIANCE MONITORING ON SOHO

First results from the VIRGO experiment (Variability of solar IRradian ce and Gravity Oscillations) on the ESA/NASA Mission SOHO (Solar and H eliospheric Observatory) are reported. The observations started mid-Ja nuary 1996 for the radiometers and sunphotometers and near the end of March for the luminosity oscillation imager. The performance of all th e instruments is very good, and the time series of the first 4-6 month s are evaluated in terms of solar irradiance variability, solar backgr ound noise characteristics and p-mode oscillations. The solar irradian ce is modulated by the passage of active regions across the disk, but not all of the modulation is straightforwardly explained in terms of s unspot flux blocking and facular enhancement. Helioseismic inversions of the observed p-mode frequencies are more-or-less in agreement with the latest standard solar models. The comparison of VIRGO results with earlier ones shows evidence that magnetic activity plays a significan t role in the dynamics of the oscillations beyond its modulation of th e resonant frequencies. Moreover, by comparing the amplitudes of diffe rent components of p-mode multiplets, each of which are influenced dif ferently by spatial inhomogeneity, we have found that activity enhance s excitation.