In order to search for empirical evidences in the transition region and corona explaining the observed variability of the chemical composition in the solar wind, we have used a set of EUV average spectra in the 296 - 1350 Angstrom wavelength range (Vernazza & Reeves 1978), to determine the relative abundances of C, N, O, Ne, Mg, Si, S in the cell centers and the network within a coronal hole and a quiet region, respectively. Moreover, we have determined the relative abundances in an active region during two periods characterized by different activity levels. The analysis has shown that the elemental abundances appear in broad 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 abundances have been found in the active region during the two considered phases. Nevetherless, we point out that the data used in this analysis for a given kind of structures, are composed by spectra taken at various times and positions within the same region, so that eventual differences may be smoothed out by temporal and spatial averages. We discuss the implications of the results concerning the cell centers and the network for the ion-neutral separation model suggested by Meyer (1991).
|Titolo:||Elemental abundances in the solar network and cell centers from EUV spectra|
|Data di pubblicazione:||1996|
|Appare nelle tipologie:||1.1 Articolo in rivista|