English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We investigate the nature of the spectral line profiles for transition regionions observed with the Interface Region Imaging Spectrograph (IRIS). In thiscontext, we have analyzed an active-region observation performed by IRIS in its1400 A spectral window. The transition-region lines are found to exhibitsignificant wings in their spectral profiles, which can be well-fitted withnon-Maxwellian kappa-distribution. The fit with a kappa-distribution canperform better than a double Gaussian fit, especially for the strongest line,Si IV 1402.8 A. Typical values of $\kappa$ found are about 2, occurring in amajority of spatial pixels where the transition region lines are symmetric,i.e., the fit can be performed. Furthermore, all five spectral lines studied(from Si IV, O IV and S IV) appear to have the same FWHM irrespective ofwhether the line is an allowed or an intercombination transition. A similarvalue of kappa is obtained for the electron distribution by fitting of the lineintensities relative to Si IV 1402.8 A, if photospheric abundances are assumed.The kappa-distributions however do not remove the presence of non-thermalbroadening. Instead, they actually increase the non-thermal width. This isbecause for kappa-distributions the transition-region ions are formed at lowertemperatures. The large observed non-thermal width lowers the opacity of the SiIV line sufficiently enough for this line to become optically thin.

Non-Maxwellian analysis of the transition-region line profiles observed by the Interface Region Imaging Spectrograph