Solar XUV limb brightening observations

Limb brightening of XUV lines of the ions Ciii Niii, Niv, Oiii, Oiv, Ov and Siiv is compared with that predicted by a modified version of a coronal model developed by Dupree and Goldberg. Systematic differences between the predicted and observed limb brightening are found. These differences can be eliminated by introducing into the model the effects of spicules that extend up into the chromospheric-coronal transition region. The spicules are assumed to be opaque to radiation between 500 and 900 Å because of absorption in the hydrogen Lyman continuum.