- Conference date: 4-9 June 2006
- Location: Auburn, Alabama (USA)
The persisting excess by about a factor of two for measured compared to calculated Stark widths of lines due to transitions between low‐lying levels of Li‐like ions ranging from B III to Ne VIII would be significantly reduced if the ratios of upper‐ to lower‐ level populations were far from local thermodynamic equilibrium (LTE). This possibility was recently discussed using a quantum‐kinetic theoretical approach by C. A. Iglesias (instead of Baranger’s earlier treatment) and applying LTE validity criteria originally proposed for one‐electron atoms or ions. However, these criteria greatly overestimate the critical electron densities required for near‐LTE for the ions of interest here, which have no transitions into n=1. Actually, recent NLTE calculations using the NOMAD code indicate steady‐state population ratios in the experiments considered here to be within 1% of LTE values in the case of B III 2s‐2p and within 5% for Ne VIII 3s‐3p transitions, thus invalidating this explanation of the discrepancies. Moreover, our calculations suggest that the electron temperatures in the B III experiment were overestimated by a factor of two. Correcting for this increases the calculated Stark widths by only about 20%. However, since much of the line emission was perhaps from outer layers with lower temperature and higher electron density, this increase may actually be by a factor of 1.6. Macroscopic Doppler effects due to radial expansion could account for the remainder of the discrepancy.
- Doppler effect
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