In the present work we have studied SUMER observations of a solar active region at the limb, to investigate the FIP bias in both cool plasma confined in the core of an active region, and in the more diffuse, unstructured hot corona surrounding them. We use lines from the high-FIP , ions, the intermediate-FIP ion, and from the low-FIP , , and ions.
We find that the Mg/Ne relative abundance is highly variable in the complex, cool core of the active region, and seems to be strongly correlated to line intensity patterns; this might suggest that each (spatially unresolved) plasma structure might have its own peculiar composition. Mg abundance enhancements relative to Ne reach up to a factor of 8.8.
The analysis of the diffuse corona seems to suggest that in off-limb active region plasma the FIP bias inside the low-FIP elements' class is dependent on the FIP value, being higher for the very-low FIP element K, although the presence of a blending line makes this conclusion uncertain. Since FIP dependent FIP bias can provide important constraints on FIP effect models, further work is recommended on this subject.
Also, we provide some evidence of height dependence of the FIP bias for K and Si, while the S results are constant with height within the uncertainties.
© European Southern Observatory (ESO) 2000
Online publication: January 29, 2001