O and Ne in an H-He Fast Solar Wind

Abstract

We have studied the abundances and ion fractions of O and Ne in an H-He fast solar wind with emphasis on gravitational settling in the chromosphere and corona. We use a time-dependent numerical model that spans the mid- to upper chromosphere, transition region, corona, and solar wind and calculates the particle density, flow velocity, parallel and perpendicular temperature, and heat flux for all particle species simultaneously. We investigate the effect of including He on the O and Ne abundances in the solar wind for two different flux tube expansion factors and find that He has a modest effect, which nevertheless becomes important for low expansion factors. The He, O and Ne abundances in the solar wind can be modulated by varying the magnetic flux tube expansion factor, but we have not been able to reproduce the observed solar wind abundances of He, O and Ne simultaneously. Furthermore, we find that unless O is heated to temperatures higher than those observed in polar coronal holes, there will be an O abundance enhancement in the corona, at about 1.6 R ☉. Finally, we find that we can reproduce the in situ ion fractions for O and Ne in H-He background solutions with a modest He heating rate, which implies a coronal He abundance of about 20-40%.