  The chemical composition of exoplanet host stars is an important factor in
understanding the formation and characteristics of their orbiting planets. The
best example of this to date is the planet-metallicity correlation. Other
proposed correlations are thus far less robust, in part due to uncertainty in
the chemical history of stars pre- and post-planet formation. Binary host stars
of similar type present an opportunity to isolate the effects of planets on
host star abundances. Here we present a differential elemental abundance
analysis of the XO-2 stellar binary, in which both G9 stars host giant planets,
one of which is transiting. Building on our previous work, we report 16
elemental abundances and compare the $\Delta$(XO-2N-XO-S) values to elemental
condensation temperatures. The $\Delta$(N-S) values and slopes with
condensation temperature resulting from four different pairs of stellar
parameters are compared to explore the effects of changing the relative
temperature and gravity of the stars. We find that most of the abundance
differences between the stars depend on the chosen stellar parameters, but that
Fe, Si, and potentially Ni are consistently enhanced in XO-2N regardless of the
chosen stellar parameters. This study emphasizes the power of binary host star
abundance analysis for probing the effects of giant planet formation, but also
illustrates the potentially large uncertainties in abundance differences and
slopes induced by changes in stellar temperature and gravity.
