Absolute Abundances in Streamers from UVCS

Details Absolute Abundances in Streamers from UVCS Absolute Abundances in Streamers from UVCS

Dec 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997esasp.415..383r&link_type=abstract

Correlated Phenomena at the Sun, in the Heliosphere and in Geospace. 31st ESLAB Symposium held 22-25 September, 1997, at ESTEC,

Physics

14

Abundances, Solar Corona, Streamers

Scientific paper

The Ultraviolet Coronagraph Spectrometer on SOHO covers the 940-1350 Angstrom range as well as the 470-630 Angstrom range in second order. It has detected coronal emission lines of H, N, O, Mg, Al, Si, S, Ar, Ca, Fe and Ni in coronal streamers. We are able to determine the ionization state and the absolute elemental abundances in the gas. There is a strong First Ionization Potential (FIP) dependence in the abundances. Oxygen is depleted relative to hydrogen, by a full order of magnitude for oxygen in the center of a quiescent streamer. Here, we extend the earlier work by considering greater heights in the streamer and by estimating the projection effects (the line of sight passing through the streamer edges). We suggest that the FIP fractionation occurs in the chromosphere, but that in addition gravitational settling produces an overall depletion at large heights in the closed-field region. We present numerical results of diffusion models.

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