Anomalous Coronal Neon Abundances in Quiescent Solar Active Regions

Abstract

The systematic di erences between the solar photospheric and coronal composition are generally thought to be related to the rst ionization potential (FIP) of the trace elements. While there are ample data showing that this is a signicant factor, there is a growing body of observational evidence that a simple, FIP-based formula is not the whole story for coronal abundances. One of the most troubling problems for the FIP-based models is the apparent abundance variation of high-FIP ([11 eV) elements with respect to one another. We describe abundance variations of (high-FIP) neon relative to (high-FIP) oxygen, and (low-FIP) iron and magnesium, in solar active region observations made by the Flat Crystal Spectrometer on the Solar Maximum Mission. We show that, even in quiescent active regions, Ne/O can vary inconsistently with simple empirical FIP models : it shows values about a factor of 2 both above and below the "" standard coronal value of 0.15 obtained from solar energetic particle measurements of long-duration events (Reames). McKenzie & Feldman have recently invoked photoionization of O I by EUV radiation to explain low measurements of the Ne/O abundance ratio. Photoionization by a longlived bath of soft X-rays and chromospheric evaporation have been suggested as being responsible for the anomalous behavior of neon in ares, but are conditions should not apply in the quiescent regions of the present study. A complex picture involving the detailed dynamics, geometry, and radiation environment in the di erentiation layer(s) may be required to understand coronal composition and its variability.