The quiet Sun extreme ultraviolet spectrum observed in normal incidence bythe SOHO coronal diagnostic spectrometer

The extreme ultraviolet quiet Sun spectrum, observed at normal incidence by the Coronal Diagnostic Spectrometer on the SOHO spacecraft, is presented. The spectrum covers the wavelength ranges 308-381 Angstrom and 513-633 Angs trom and is based on data recorded at various positions on the solar disk b etween October 1996 and February 1997. Datasets at twelve of these 'positio ns' were judged to be free from active regions and data faults and selected for detailed study. A constrained maximum likelihood spectral line fitting code was used to analyse the spectral features. In all over 200 spectrum l ines have been measured and about 50% identified. The line identification p rocess consisted of a number of steps. Firstly assignment of well known lin es was made and used to obtain the primary wavelength calibration. Variatio ns of wavelengths with position were used to assess the precision of calibr ation achievable. Then, an analysis method first used in studies with the C HASE experiment, was applied to the new observations. The behaviour of the intensities of lines from like ions over the twelve positions, called 'posi tion patterns', were used to distinguish probable emitters of weaker lines and extend the identifications. Spectral line widths and expected multiplet intensities were examined to identify lines and probable blends. The produ ct of the study is a table which includes all clearly observed emission lin es, their measured wavelengths, widths and count rates. Adopted laboratory wavelengths, ion and transition designations are also presented for identif ied lines. The table has an estimate of the uncertainty of the count rates based on a statistical analysis of the variability of each line. A marked s pectrum is also provided.