  We present two Keck HIRES spectra (R=40,000) of a bulge K3 giant taken on
successive nights during the second caustic crossing of the binary microlensing
event EROS BLG-2000-5. This caustic crossing served to effectively resolve the
surface of the source star: the spectrum from the second night is dominated by
the limb, while the spectrum from the first night is comprised of light from a
broader range of radii. To demonstrate that the spectra are adequate to resolve
the differences between them, we analyze the H-alpha line. The equivalent width
is ~8% smaller on the second night, and the signal-to-noise ratio per
resolution element (165 and 75 on the two nights respectively) is sufficient to
show that the difference is approximately constant over the ~2A (~15 resolution
element) extent of the line. The sign of the difference is in the expected
direction since the limb is the coolest part of the star and therefore should
have the weakest H-alpha. We invite atmosphere modelers to predict the
difference spectrum from the entire spectral range 5500<lambda<7900A so that
these predictions can be compared to our observations.
