ADAS workshop, Auburn University Anomalous O IV line ratios in the solar spectrum Alessandra Giunta 07-10-11 ADAS workshop, Auburn University

O IV lines in the solar spectrum SoHO/SUMER Intensity Wavelength/Å SoHO/CDS Intensity Wavelength/Å Hinode/EIS Intensity Wavelength/Å 07-10-11 ADAS workshop, Auburn University

ADAS workshop, Auburn University Problem Muglach et al. (2010) found that the measured O IV I(787.7 Å)/I(279.9 Å) ratio is lower than the predicted ratio by a factor 2-5 and the derived electron temperature is in the range of logT=5.58-6.07, much higher than the formation temperature in ionisation equilibrium. ▪ They used: - observations taken during SUMER/EIS campaign in April 2007 - atomic data from CHIANTI v. 5.2.1. ▪ They investigated various possible causes: - instrumental and observational effects - presence of additional processes (photo-excitation, self-absorption, non-Maxwellian distribution). ▪ They did not solve the discrepancy, with the implication that non equilibrium ionisation state may be present. 07-10-11 ADAS workshop, Auburn University

ADAS workshop, Auburn University Approach ▪ A new observational data set taken during the joint SUMER/CDS/EIS campaign of April 2009 is explored. ▪ The ratio I(787.7 Å)/I(279.9 Å) is re-examined and other three O IV ratios are investigated: - I(554.5Å)/I(279.9 Å) temperature dependent - I(787.7 Å)/I(554.5 Å) temperature dependent - I(787.7 Å)/I(b790 Å) temperature independent ▪ The atomic data for these ratios are revised comparing three datasets: - CHIANTI v. 5.2.1 - Revised (CHIANTI + Sampson, 1995) - Aggarwal & Keenan (2008) 07-10-11 ADAS workshop, Auburn University

ADAS workshop, Auburn University Observational domain ▪ Observational data taken from SUMER, CDS and EIS have been calibrated using the standard procedures. ▪ The co-alignment has been done using common emission lines or lines emitted from the same ion. ▪ The cross-calibration has been performed through direct line comparison and spectroscopic methods. ▪ The observed R=I(787.7 Å)/I(279.9 Å) ratio obtained is: logR=1.8 (the intensity units are photons cm-2 s-1) 07-10-11 ADAS workshop, Auburn University

ADAS workshop, Auburn University Atomic domain Three atomic datasets are examined: ▪ CHIANTI ▪ Revised ▪ Aggarwal & Keenan (2008) CHIANTI The main source for the effective collision strengths (Y-values) is Zhang et al. (1994) for the first 15 levels and Sampson (1995) for the other 110 levels. However only transitions which involve the first 5 levels are included in the model. A-value for transitions amongst levels from 6 to 15 are also included, but not the corresponding Y-values. Revised This dataset has been built up merging the CHIANTI data with the DW calculations of Sampson to add the whole set of missing Y-values. Aggarwal & Keenan (2008) These are the most recent R-matrix calculations for O3+ available in literature and include transitions which involve the n=4 levels. 07-10-11 ADAS workshop, Auburn University

Atomic data comparison The main difference lies in the population of the upper level (2s23s 2S1/2), called N279, from which the line at 279.9 Å originates. rv = Revised ch = CHIANTI ak = Aggarwal & Keenan 07-10-11 ADAS workshop, Auburn University

ADAS workshop, Auburn University Results Comparison between the observed and theoretical values for the ratio I(787.7 Å)/I(279.9 Å). The electron temperature derived in this work is logT=5.17-5.39, close to the temperature expected under the assumption of ionisation equilibrium. rv = Revised ch = CHIANTI ak = Aggarwal & Keenan logT=5.58-6.07 logT=5.17-5.39 formation temperature 07-10-11 ADAS workshop, Auburn University

Other line ratio comparison Temperature dependent line ratios As further check, the three other O IV ratios are illustrated, comparing the measurements with theoretical data. Since the discrepancy is caused by the intensity of the line at 279.9 Å, the I(554.5Å)/I(279.9 Å) ratio shows the same behaviour as I(787.7Å)/I(279.9 Å), unlike the other two ratios. I(554.5Å)/I(279.9 Å) Temperature independent line ratio logT=5.17 I(787.7 Å)/I(b790 Å) I(787.7 Å)/I(554.5 Å) rv = Revised ch = CHIANTI ak = Aggarwal & Keenan 07-10-11 ADAS workshop, Auburn University

ADAS workshop, Auburn University Discussion The Muglach et al. (2010) O IV discrepancy has been solved, however some issues arise from this work: ▪ the uncertainties of atomic data and model can affect substantially the interpretation of the observed emission ▪ the completeness (complete system of A-values and Y-values) and top-up does matter in the population model ▪ new R-matrix calculation for O3+ are desirable to add more confidence in the currently available atomic data. 07-10-11 ADAS workshop, Auburn University