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 Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

Context: The sharp temperature and density gradients in the coronaltransition region are a challenge for models and observations.  Aims: We set out to get linearly- and quadratically-weighted average electrondensities in the region emitting the S VI lines, using the observed opacity andthe emission measure of these lines.  Methods: We analyze SoHO/SUMER spectroscopic observations of the S VI lines,using the center-to-limb variations and radiance ratios to derive the opacity.We also use the Emission Measure derived from radiance at disk center.  Results: We get an opacity at S VI line center of the order of 0.05. Theresulting average electron density is 2.4 10^16 m^-3 at T = 2 10^5 K. Thisvalue is higher than the values obtained from radiance measurements.Conversely, taking a classical value for the density leads to a too high valueof the thickness of the emitting layer.  Conclusions: The pressure derived from the Emission Measure method compareswell with previous determinations and implies a low opacity of 5 10^-3 to10^-2. The fact that a direct derivation leads to a much higher opacity remainsunexplained, despite tentative modeling of observational biases. Furthermeasurements need to be done, and more realistic models of the transitionregion need to be used.

Electron density in the quiet solar coronal transition region from SoHO/SUMER measurements of S VI line radiance and opacity