The Relative Abundance Of Chromium And Iron In The Solar Wind

Chromium and iron are two heavy elements in the solar wind with similar masses. The MTOF (Mass Time Of Flight) sensor of the CELIAS investigation on the SOHO spacecraft easily allows these two elements to be resolved from one another. Taking the ratio of the densities of these two elements - as opposed to considering their absolute abundances - minimizes the effects of uncertainties in instrument efficiency. Measurements of the abundance ratio are presented here. The First Ionization Potential (FIP) of chromium is 6.76 eV, while the FIP of iron is 7.87 eV. Since Cr and Fe have similar FIPs the ratio of their abundances should not be biased by the FIP effect which is well known in different solar wind flows. Therefore the Cr/Fe ratio from the MTOF data should give a good measure of the photospheric abundance ratio. We also compare the ratio measured in this work to the meteoritic value.