ELEMENTAL ABUNDANCES IN THE SOLAR NETWORK AND CELL CENTERS FROM EUV SPECTRA

In order to search for empirical evidences in the transition region an d corona explaining the observed variability of the chemical compositi on in the solar wind, we have used a set of EUV average spectra in the 296 - 1350 Angstrom wavelength range (Vernazza & Reeves 1978), to det ermine the relative abundances of C, N, O, Ne, Mg, Si, S in the cell c enters and the network within a coronal hole and a quiet region, respe ctively. Moreover, we have determined the relative abundances in an ac tive region during two periods characterized by different activity lev els. The analysis has shown that the elemental abundances appear in br oad agreement with the photospheric ones for all the different regions examined. Moreover, within the coronal hole and the quiet region, the chemical composition in the cell centers does not differ appreciably from that in the network. Further, no differences in the elemental abu ndances have been found in the active region during the two considered phases. Nevetherless, we point out that the data used in this analysi s for a given kind of structures, are composed by spectra taken at var ious times and positions within the same region, so that eventual diff erences may be smoothed out by temporal and spatial averages. We discu ss the implications of the results concerning the cell centers and the network for the ion-neutral separation model suggested by Meyer (1991 ).