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Astron. Astrophys. 360, 1148-1156 (2000)

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The effect of different ion fraction datasets on plasma diagnostics

D. Gianetti 1, E. Landi 2,1 and M. Landini 1

1 University of Florence, Dipartimento di Astronomia e Scienza dello Spazio, Italy
2 Max-Planck-Institut für Aeronomie, Katlenburg-Lindau, Germany

Received 5 May 2000 / Accepted 6 July 2000


In the present work the element abundances in an active region observed on the solar disk are studied using EUV spectral lines observed by the Coronal Diagnostic Spectrometer (CDS) on board of SOHO. Making use of the large number of lines identified in the CDS spectral range and of the instrument imaging capability, the abundances of several elements having First Ionization Potential (FIP) smaller and greater than 10eV have been determined in different parts of the observed active region. Also, the differential emission measure of the selected emitting regions have been determined.

This study has been carried out assuming ionization equilibrium in the emitting plasma, and adopting three different ion fraction datasets to interpret the observed intensities. This has permitted a detailed check of the impact of differences in the ion fraction datasets on the element abundances measurements and DEMdetermination and to assess the reliability of the use of EUV line intensities for such studies.

Our results show that the use of different ion fractions may alter significantly the measured abundances and DEMcurves, and have large effects on quantitative FIP effect studies.

Key words: plasmas – Sun: abundances – Sun: activity – Sun: UV radiation

Send offprint requests to: E. Landi (enricol@arcetri.astro.it)

© European Southern Observatory (ESO) 2000

Online publication: August 23, 2000