UVCS/SOHO Observations of Spectral Line Profiles in Polar Coronal Holes

摘要

Ultraviolet emission line profiles have been measured on 15-29 September 1997 for H 1 1216 A, OVI 032, 1037 A and Mg X 625 A in a polar coronal hole, at heliographic heights #rho# (in solar radii) between 1.34 and 2.0. Observations of H I 1216 A and the O VI doublet from January 1997 for #rho# = 1.5 to 3.0 are provided for comparison. Mg X 625 A is observed to have a narrow component at #rho# = 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 #rho# = 1.34, but are significantly larger at #rho# = 1.5 and much larger for #rho# > 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 #rho# = 2.0, but never reach the values of O VI.