Can the Composition of the Solar Corona Be Derived from Hinode/Extreme-Ultraviolet Imaging Spectrometer Spectra?
Elemental abundances appear to be the same everywhere in the photosphere, but in the solar corona they vary in different regions. Abundances in quiet Sun (closed) flux tubes are different from those in coronal hole (CH, open) magnetic field regions, and therefore abundance variations might possibly be used to determine locations of slow and fast solar wind in the corona. In active regions, abundances can change from region to region and can vary with the age of the region. In the present paper, we evaluate the feasibility of determining relative elemental abundances in the corona using spectra acquired by the Extreme-ultraviolet Imaging Spectrometer (EIS) on Hinode. As test cases, we attempt to evaluate the coronal composition above the limb in an equatorial quiet region and in a polar CH. We also determine the elemental composition of coronal regions with moderate activity on the disk and at the limb. To estimate the accuracy of the instrumental calibration and the atomic physics used in the calculations, we compare the derived composition with earlier derivations from spectra recorded by the Solar Ultraviolet Measurements of Emitted Radiation spectrometer in similar regions. We find that EIS can be used to determine relative abundance variations in the inner solar corona. The determination of absolute abundances can also be attempted after additional calibrations in space are accomplished.