VIRGO Scientific Objectives

The VIRGO experiment will provide the following observational and derived data:

• continuous high-precision, high-stability and high-accuracy measurements of the solar total and spectral irradiance and spectral radiance variation;
• continuous measurements of the solar polar and equatorial diameters;
• frequencies, amplitudes and phases of oscillation modes in the frequency range of 1 microHz to 8 mHz;

The total irradiance is measured with active cavity radiometers (PM06-V and the Dual Irradiance Absolute Radiometer, DIARAD), the spectral irradiance by three-channel Sunphotometers (SPM) and the radiance with 12 resolution elements on the solar disk using the Luminosity Oscillations Imager (LOI). These data will be utilized to achieve the main scientific objectives of VIRGO summarized in the following list:

• detect and classify low-degree g modes of solar oscillations;
• determine the sound speed, density stratification and rotation in the solar interior, specifically determine the physical and dynamical properties of the solar core;
• study the solar atmosphere through comparison of amplitudes and phases of the p modes with these from GOLF (Global Oscillations at Low Frequencies) and SOI/MDI (Solar Oscillation Investigation/Michelson Doppler Imager);
• search for the long periodicities or quasiperiodicities that have been found in other solar parameters;
• utilize the solar `noise' signal to develop models for the global signature of stellar surface parameters;
• determine properties of the solar asphericity and its variation in time;
• study the relation between p-mode frequency changes and irradiance variations;
• study the influence of solar active regions and other large-scale structures on total and spectral irradiance;
• study the solar energy budget;
• provide accurate total and spectral irradiance data for input in terrestrial climate modelling.

If you want more information, you can retrieve the Science Book of VIRGO, the so called Purple Book (Warning: its size is 90 kbytes!). There you will find more informations on the scientific objectives, and on the instruments composing the VIRGO payload.

Last updated by Thierry Appourchaux on Wenesday, June 9, 1995 at 9:17