Electron density in the quiet solar coronal transition region from SoHO-SUMER measurements of S VI line radiance and opacity - Astrophysics > Solar and Stellar AstrophysicsReport as inadecuate




Electron density in the quiet solar coronal transition region from SoHO-SUMER measurements of S VI line radiance and opacity - Astrophysics > Solar and Stellar Astrophysics - Download this document for free, or read online. Document in PDF available to download.

Abstract: 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.



Author: E. Buchlin, J.-C. Vial

Source: https://arxiv.org/







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