SOLAR TRANSITION REGION LINES OBSERVED BY THE INTERFACE REGION IMAGING SPECTROGRAPH: DIAGNOSTICS FOR THE OIV AND SI IV LINES

作者：Dudik J; Del Zanna G; Dzifcakova E; Mason H E; Golub L

来源：Astrophysical Journal Letters, 2014, 780(1): L12.

DOI：10.1088/2041-8205/780/1/L12

• atomic data
• atomic processes
• radiation mechanisms: non-thermal
• Sun: transition region
• Sun: UV radiation

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 kappa-distribution exhibiting a high-energy tail. The SI IV lines are formed at lower temperatures than the O IV lines for all kappa. In non-Maxwellian situations with lower kappa, 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 kappa is investigated and it is found that the O IV 1404.78 angstrom/1399.77 angstrom ratio provides a good density diagnostics except for very low T combined with extreme non-Maxwellian situations.

• 出版日期2014-1-1