Submitted abstract to the 24th General Essembly in Den Hague, Netherlands, April 19-23, 1999.
The isotopic composition of solar system material provides knowledge about the origin of the elements in stars and the formation and history of the solar system. Furthermore, from these measurements one obtains information on the isotopic composition of the outer convective zone of the Sun. Two different source regions of the solar wind can be distinguished on the Sun. The slow solar wind originating from closed field line regions, has a slow bulk velocity and high thermal temperature, and the high speed solar wind which has a low thermal temperature and originates from coronal holes. Data from the high resolution Mass Time-of-Flight spectrometer MTOF on board SOHO have been accumulated for time periods in which coronal hole or non-coronal hole type plasma has been detected in order to determine the abundance ratios of magnesium isotopes in these two different source regions.