1. ADAS workshop, Auburn University
Anomalous O IV line ratios
in the solar spectrum
Alessandra Giunta
ADAS workshop, Auburn University

2. O IV lines in the solar spectrum
SoHO/SUMER
Intensity
Wavelength/Å
SoHO/CDS
Intensity
Wavelength/Å
Hinode/EIS
Intensity
Wavelength/Å
ADAS workshop, Auburn University

3. 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= , 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
▪ 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.
ADAS workshop, Auburn University

4. 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
- Revised (CHIANTI + Sampson, 1995)
- Aggarwal & Keenan (2008)
ADAS workshop, Auburn University

5. 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)
ADAS workshop, Auburn University

6. 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.
ADAS workshop, Auburn University

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

8. 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= , close to the temperature expected under the assumption of ionisation equilibrium.
rv = Revised
ch = CHIANTI
ak = Aggarwal & Keenan
logT=
logT=
formation
temperature
ADAS workshop, Auburn University

9. 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 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
ADAS workshop, Auburn University

10. 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.
ADAS workshop, Auburn University