  We present measurements of relative elemental abundances in plumes and
interplumes. Plumes are bright, narrow structures in coronal holes that extend
along open magnetic field lines far out into the corona. Previous work has
found that in some coronal structures the abundances of elements with a low
first ionization potential (FIP) < 10 eV are enhanced relative to their
photospheric abundances. This coronal-to-photospheric abundance ratio, commonly
called the FIP bias, is typically 1 for element with a high-FIP (> 10 eV). We
have used EIS spectroscopic observations made on 2007 March 13 and 14 over an
~24 hour period to characterize abundance variations in plumes and interplumes.
To assess their elemental composition, we have used a differential emission
measure (DEM) analysis, which accounts for the thermal structure of the
observed plasma. We have used lines from ions of iron, silicon, and sulfur.
From these we have estimated the ratio of the iron and silicon FIP bias
relative to that for sulfur. From the results, we have created FIP-bias-ratio
maps. We find that the FIP-bias ratio is sometimes higher in plumes than in
interplumes and that this enhancement can be time dependent. These results may
help to identify whether plumes or interplumes contribute to the fast solar
wind observed in situ and may also provides constraints on the formation and
heating mechanisms of plumes.

Solar and Stellar Astrophysics