The off-limb behavior of the first ionization potential effect in T > 5 x 10(5) K solar plasmas

We investigate the behavior of the solar first ionization potential (FIP) e ffect (the abundance enhancement of elements with first ionization potentia l of less than 10 eV in the corona with respect to photospheric values) wit h height above the limb in a region of diffuse quiet corona observed by the SUMER instrument on SOHO, with emphasis on so-called upper transition regi on lines. Previous disk observations have shown different abundance pattern s in emission from lines at temperatures above and below similar to 8 x 10( 5) K, with an FIP effect clearly visible at the higher temperatures and les s so at the lower temperatures. Our initial aim is to determine whether suc h a difference is also visible in off-limb observations. We find a low-FIP element enhancement of a factor of 3-4 indicated in all line ratios. The Mg vn 868.11/Ne VII 895.17 ratio is also seen to decrease toward a photospher ic value when tracked down from the corona to the limb. This is markedly di fferent from the behavior of higher temperature line ratios and may be rela ted to the differing heating and mass supply mechanisms for plasmas at temp eratures above and below similar to 8 x 10(5) K. An additional unexpected feature of our observations is that in low-FIP/hig h-FIP line ratios formed at temperatures close to the freeze-in temperature of the fast solar wind (similar to 10(6) K), there is also a small diminut ion of the FIP enhancement at the highest altitudes observed in this study. We discuss the possible relevance of this to the origin of the fast solar wind.