ISOTOPIC COMPOSITION OF SOLAR-WIND CALCIUM - FIRST IN-SITU MEASUREMENT BY CELIAS MTOF ON BOARD SOHO/

We present the first results of the Ca isotopic abundances derived fro m the high-resolution Mass Time-of-Flight (MTOF) spectrometer of the C harge, Element, and Isotope Analysis System (CELIAS) experiment on boa rd the Solar and Heliospheric Observatory (SOHO). We obtain the isotop ic ratios Ca-40/Ca-42 = 128 +/- 47 and Ca-40/Ca-44 = 50 +/- 8, consist ent with terrestrial values. This is the first in situ determination o f the solar wind calcium isotopic composition and is important for stu dies of stellar modeling and solar system formation since the present- day solar Ca isotopic abundances are unchanged from their original iso topic composition in the solar nebula.