Authors: Alexandros Koukras (Columbia University), Michael Hahn (Columbia University), Daniel W. Savin (Columbia University)

The fast solar wind originates from regions of open magnetic field in the Sun, which are called coronal holes; but the origin of the slow solar wind is still not well understood. The in-situ measured elemental abundances of the slow solar wind suggest that it originates from initially closed field lines. Consequently, several theories propose that the boundaries of coronal holes are the source region of the slow solar wind. Magnetic reconnection of quite sun loops with the open field lines at the boundaries of coronal holes could also explain the apparent rigid rotation of coronal holes.
Our aim is to quantify the relative abundances of different elements at the boundaries of coronal holes. Reconnection is expected to modulate these abundances through the First Ionization Potential (FIP) effect. We will measure the FIP effect across coronal hole boundaries as a function of latitude on the leading and trailing edges and quantify any difference.
For our analysis we use spectroscopic data from EIS on Hinode. The wide wavelength range that it covers makes it suitable for FIP effect diagnostics. Our methodology for the FIP analysis accounts for the temperature structure of the observed region. To accomplish that we compute the differential emission measure (DEM), based on the observed line intensities of low FIP elements like iron and silicon. We then use that DEM to predict the intensity of lines from other elements, such as sulfur. Comparing the modeled to observed intensities allows us to infer the FIP bias between the coronal and photospheric abundances. We have performed the above analysis for each pixel in the EIS field of view, which allows us to produce FIP bias maps at the boundaries of coronal holes.