Solar Transition-Region Lines Observed by the Interface Region Imaging Spectrograph: Diagnostics for the O IV and Si IV Lines

0399493 - ASÚ 2015 RIV US eng J - Journal Article
Dudík, Jaroslav - Del Zanna, G. - Dzifčáková, Elena - Mason, H. E. - Golub, L.
Solar Transition-Region Lines Observed by the Interface Region Imaging Spectrograph: Diagnostics for the O IV and Si IV Lines.
Astrophysical Journal Letters. Roč. 780, č. 1 (2014), L12/1-L12/7. ISSN 2041-8205. E-ISSN 2041-8213
R&D Projects: GA ČR GAP209/12/1652
Grant - others:SAV(SK) Vega1/ 240/11
Institutional support: RVO:67985815
Keywords : atomic data * atomic processes * radiation mechanisms
Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics
Impact factor: 5.339, year: 2014

The formation of the transition region O IV and Si IV lines observable by the Interface Region Imaging Spectrograph (IRIS) is investigated for both Maxwellian and non-Maxwellian conditions characterized by a κ-distribution exhibiting a high-energy tail. The Si IV lines are formed at lower temperatures than the O IV lines for all κ. In non-Maxwellian situations with lower κ, the contribution functions are shifted to lower temperatures. Combined with the slope of the differential emission measure, it is possible for the Si IV lines to be formed at very different regions of the solar transition region than the O IV lines; possibly close to the solar chromosphere. Such situations might be discernible by IRIS. It is found that photoexcitation can be important for the Si IV lines, but is negligible for the O IV lines. The usefulness of the O IV ratios for density diagnostics independently of κ is investigated and it is found that the O IV 1404.78 Å/1399.77 Å ratio provides a good density diagnostics except for very low T combined with extreme non-Maxwellian situations.
Permanent Link: http://hdl.handle.net/11104/0230518