The Effect of High‐lying Levels on Atomic Models Relevant to Spectroscopic Analyses of Solar Extreme‐Ultraviolet Spectra

Abstract

In this work we investigate the effect of including high-lying configurations in the collisional-radiative models used to calculate spectral line intensities recorded by the Solar Ultraviolet Measurement of Emitted Radiation (SUMER) spectrometer on board the SOHO satellite. Many of the emission lines observed by SUMER are attributed to transitions within the L and M electronic shells of ions isoelectronic to sequences from Li i to Na i. By using atomic data that are mostly generated by the Hebrew University Lawrence Livermore Atomic Code (HULLAC), we incorporate in the atomic models configurations from higher shells and systematically study their effect on the calculated line intensities in selected ions. The high-lying configurations alter the line intensities through radiative cascades and configuration interaction effects. We find that cascades can significantly enhance the line intensities of the considered ions by up to 60% at temperatures of the ion maximum fractional abundance. The enhancement due to cascades increases with increasing temperature and charge state. The configuration mixing effects can either enhance or reduce the line intensities. Generally, the mixing effect becomes less important for higher charge states.

Emission lines of Na-like ions in spectra obtained with the Solar EUV Research Telescope and Spectrograph (SERTS)

“…Energies for these were taken from Moore (1971), Corliss & Sugar (1982) and Shirai et al (1987) for Ar viii , Fe xvi and Ni xviii , respectively, and Sampson et al (1990) for all other ions. Test calculations including higher‐lying levels were found to have a negligible effect on the theoretical line ratios considered in this paper, as also found by Doron et al (2002).…”

“…In summary, our analysis of the SERTS data sets reveal generally very good agreement between theory and observation for the Na‐like ion transitions present in the spectra, indicating that the lines are reliably detected and are not seriously affected by blending. Most of the Na‐like ion emission features may therefore be employed with confidence in solar spectral analyses, such as abundance studies (Doron et al 2002).…”

Astrophysics in 2002

“…Even larger enhancement factors were measured in a CMEproducing active region, i.e., first ionization potential enhancements of 7-8 compared with the usual factor of 3-4 (Ciaravella et al 2002). Atomic physics parameters used in solar physics have been steadily improved, by measurements of the resonance strengths and energies for dielectronic recombination (Savin & Laming 2002), high-lying electronic shells (Doron et al 2002), escape probabilities and absorption factors (Fischbacher et al 2002), modeling of observed S xii and Fe xxi lines (Keenan et al 2001(Keenan et al , 2002a(Keenan et al , 2002b, Fe xiii lines (Landi 2002), and Fe xxv (Dzifcakova & Kulinova 2001). Major progress cumulated in the fourth release and update of the atomic database CHIANTI (Landi et al 2002a(Landi et al , 2002b, which contains atomic data over the entire wavelength range of A ˚.…”

Temperature Measurements in the Solar Transition Region Using NiiiLine Intensity Ratios

“…In O iv the required excitation energy for the 2p 3 levels is $32 eV, whereas for the 2s2p 2 levels it is only $16 eV. A good aspect of the line ratios we have chosen is that the upper levels in the numerator, 2p 3 , are not populated significantly by cascades, at least not at temperatures close to the temperature of the ion maximum abundance (Doron et al 2002). This is a distinct advantage because, normally, level populations resulting from weak excitations are more sensitive to other mechanisms such as cascades.…”