EUV Spectral Line Profiles in Polar Coronal Holes from 1.3 to 3.0 R_solar

Abstract

Spectral line profiles have been measured for H I λ1216, O VI λλ1032, 1037, and Mg X λ625 in a polar coronal hole observed during 1997 September 15-29, at projected heliographic heights ρ between 1.34 and 2.0 R_solar. Observations of H I λ1216 and the O VI doublet from 1997 January for ρ=1.5-3.0 R_solar are provided for comparison. The O VI lines are well fit to a narrow and broad component which appear to be associated with regions of higher and lower spectral radiance, respectively. The narrow components dominate at low heights and become a small fraction of the lines at higher heights. Mg X λ625 is observed to have a narrow component at ρ=1.34 R_solar which accounts for only a small fraction of the observed spectral radiance. In the case of the broad components, the values of v_1/e for O VI are only slightly larger than those for H I at ρ=1.34 R_solar but are significantly larger at ρ=1.5 R_solar and much larger for ρ>1.75 R_solar. 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 R_solar but never reach the values of O VI.