UVCS/SOHO Observations of Spectral Line Profiles in Polar Coronal Holes
Cranmer, S. R.; Modigliani, A.; Ciaravella, A.; Fineschi, S.; Noci, G.; Kohl, J. L.; Gardner, L. D.; Esser, R.; Suleiman, R.
United States, Italy
Abstract
Ultraviolet emission line profiles have been measured on 15-29 September 1997 for H I 1216 Å, O VI 1032, 1037 Å and Mg X 625 Å in a polar coronal hole, at heliographic heights ϱ (in solar radii) between 1.34 and 2.0. Observations of H I 1216 Å and the O VI doublet from January 1997 for ϱ = 1.5 to 3.0 are provided for comparison. Mg X 625 Å is observed to have a narrow component at ϱ = 1.34 which accounts for only a small fraction of the observed spectral radiance, and a broad component that exists at all observed heights. The widths of O VI broad components are only slightly larger than those for H I at ϱ = 1.34, but are significantly larger at ϱ = 1.5 and much larger for ϱ > 1.75. In contrast, the Mg X values are less than those of H I up to 1.75 and then increase rapidly up to at least ϱ = 2.0, but never reach the values of O VI.