Electron Density of Active Region Outflows Measured by the EUV Imaging Spectrometer on board Hinode

Abstract

In order to better understand the nature of active region outflows, the electron density was measured by using a density-sensitive line pair, Fe xiv 264.78 Å/274.20 Å. Because coronal line profiles of the outflow region are composed of a major component with a Doppler shift of ≤slant 10 km {{s}^-1} and a minor component (enhanced blue wing, EBW) blueshifted by up to 100 km {{s}^-1}, we extracted EBW from the line profiles through double-Gaussian fitting. We tried applying the simultaneous fitting to those two Fe xiv lines with several physical restrictions. Electron density for both components ({{n}_Major} and {{n}_EBW}, respectively) was calculated by referring to the theoretical intensity ratio as a function of electron density as per the CHIANTI database. We studied six locations in the outflow regions around NOAA AR10978. The average electron density was {{n}_Major}={{10}^{9.16+/- 0.16}} c{{m}^-3} and {{n}_EBW}={{10}^{8.74+/- 0.29}} c{{m}^-3}. The magnitude relationship between {{n}_Major} and {{n}_EBW} was the opposite in the eastern and western outflow regions. The column depth was also calculated for each component, which leads to the result that the outflows possess only a small fraction (∼0.1) in the eastern region, whereas they dominate over the major component in the line profiles by a factor of five in the western region. When taking into account the extended coronal structures, the western region can be thought to represent the mass leakage. In contrast, we suggest a possibility that the eastern region actually contributes to mass supply to coronal loops.