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Recent solar spectroscopic observations have shown that coronal spectrallines can exhibit asymmetric profiles, with enhanced emissions at their bluewings. These asymmetries correspond to rapidly upflowing plasmas at speedsexceeding ~ 50 km/s. Here, we perform a study of the density of the rapidlyupflowing material and compare it to that of the line core which corresponds tothe bulk of the plasma. For this task we use spectroscopic observations ofseveral active regions taken by the Extreme Ultraviolet Imaging Spectrometer ofthe Hinode mission. The density sensitive ratio of the Fe XIV lines at 264.78and 274.20 A is used to determine wing and core densities. We compute the ratioof the blue wing density to the core density and find that most values are oforder unity. This is consistent with the predictions for coronal nanoflares ifmost of the observed coronal mass is supplied by chromospheric evaporationdriven by the nanoflares. However, much larger blue wing-to-core density ratiosare predicted if most of the coronal mass is supplied by heated materialejected with type II spicules. Our measurements do not rule out a spiculeorigin for the blue wing emission, but they argue against spicules being aprimary source of the hot plasma in the corona. We note that only about 40% ofthe pixels where line blends could be safely ignored have blue wing asymmetriesin both Fe XIV lines. Anticipated sub-arcsecond spatial resolutionspectroscopic observations in future missions could shed more light on theorigin of blue, red, and mixed asymmetries.

Core and Wing Densities of Asymmetric Coronal Spectral Profiles: Implications for the Mass Supply of the Solar Corona