We report low resolution near infrared spectroscopic observations of the
eruptive star FU Orionis using the Integral Field Spectrograph Project 1640
installed at the Palomar Hale telescope. This work focuses on elucidating the
nature of the faint source, located 0.5" south of FU Ori, and identified in
2003 as FU Ori S. We first use our observations in conjunction with published
data to demonstrate that the two stars are indeed physically associated and
form a true binary pair. We then proceed to extract J and H band
spectro-photometry using the damped LOCI algorithm, a reduction method tailored
for high contrast science with IFS. This is the first communication reporting
the high accuracy of this technique, pioneered by the Project 1640 team, on a
faint astronomical source. We use our low resolution near infrared spectrum in
conjunction with 10.2 micron interferometric data to constrain the infrared
excess of FU Ori S. We then focus on estimating the bulk physical properties of
FU Ori S. Our models lead to estimates of an object heavily reddened, A_V
=8-12, with an effective temperature of ~ 4000-6500 K . Finally we put these
results in the context of the FU Ori N-S system and argue that our analysis
provides evidence that FU Ori S might be the more massive component of this
binary syste