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Looking for the FIP Effect in EUV Spectra: Examining the Solar Case

Published online by Cambridge University Press:  12 April 2016

Bernhard Haisch ,
Julia L. R. Saba  and
Jean-Paul Meyer
Bernhard Haisch
Affiliation:
Lockheed Solar and Astrophysics Laboratory, Dept. 91-30, Bldg. 252, 3251 Hanover St., Palo Alto, CA 94304, USA
Julia L. R. Saba
Affiliation:
Lockheed Solar and Astrophysics Laboratory, Dept. 91-30, Bldg. 252, 3251 Hanover St., Palo Alto, CA 94304, USA stationed at Solar Data Analysis Center, Code 682.2, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
Jean-Paul Meyer
Affiliation:
Service dAstrophysique, CEA/DSM/DAPNIA, Centre d’Etudes de Saclay, 91191 Gif-sur-Yvette, France

Abstract

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Systematic differences between elemental abundances in the corona and in the photosphere have been found in the Sun. The abundance anomalies are correlated with the first ionization potentials (FIP) of the elements. The overall pattern is that low-FIP elements are preferentially enhanced relative to high-FIP elements by about a factor of four; the transition occurs at about 10 eV. This phenomenon has been measured in the solar wind and solar energetic particle composition, and in EUV and X-ray spectra of the corona and flares. The FIP effect should eventually offer valuable clues into the process of heating, ionization and injection of material into coronal and flaring loops for the Sun and other stars. The situation for the Sun is remarkably complex: substantial abundance differences occur between different types of coronal structures, and variations occur over time in the same region and from flare to flare. Anomalies such as enhanced Ne/O ratios, distinctly at odds with the basic FIP pattern, have been reported for some flares. Are the high-FIP elements underabundant or the low-FIP elements overabundant with respect to hydrogen? This issue, which has a significant impact in physical interpretation of coronal spectra, is still a subject of controversy and an area of vigorous research.

Type
XII. The Solar/Stellar Connection in the EUV
Information
International Astronomical Union Colloquium , Volume 152: Astrophysics in the Extreme Ultraviolet , 1996 , pp. 511 - 518
Copyright
Copyright © Kluwer 1996

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