Abstract

This spatial experiment is under construction and has been defined as a 2 years mission on board SOHO, a satellite dedicated to the Sun which will be launched in mid 95. The main objectives are the detection of solar low degree acoustic modes and solar gravity modes for improving our knowledge of the solar nuclear region.

Introduction

The spatial experiment, GOLF (Global oscillations at Low Frequencies), has been accepted by ESA in March 1988 and should be boarded on the SOHO (SOlar and Heliospheric Observatory) satellite (Damé et al 1988, Gabriel et al 1989). This satellite will be launched by NASA in mid 1995. The objectives of this experiment is to enhance our knowledge of the solar interior by the measurement of the low degree acoustic modes: 1=0, 1, 2, 3, i.e the most penetrating ones, and by the possible measurement of the gravity modes. These different types of modes correspond to frequencies between some 10−6 and 8 10−3 Hz. On the same satellite there will be two other helioseismic experiments: VIRGO and MDI, the first one is a variability solar irradiance measurement in different wavelengths which allows to reach acoustic modes of degree 1= 0, 7. The second one, using a Michelson Doppler imager, is a complementary experiment which must be able to detect degree acoustic modes up to 1= 4500.

The success of such mission is largely dependent on the stability of the measurements, which requires a pointing stability of the satellite better than 1 arc sec per 15 minutes.