  We present the first orbital elements for the massive close binary, HD
101131, one of the brightest objects in the young, open cluster, IC 2944. This
system is a double-lined spectroscopic binary in an elliptical orbit with a
period of 9.64659 +/- 0.00012 days. It is a young system of unevolved stars
(approximately 2 million years old) that are well within their critical Roche
surfaces. We use a Doppler tomography algorithm to reconstruct the individual
component optical spectra, and we apply well known criteria to arrive at
classifications of O6.5 V((f)) and O8.5 V for the primary and secondary,
respectively. We compare the reconstructed spectra of the components to single
star, spectrum standards to determine a flux ratio of f_2/f_1 = 0.55 +/- 0.08
in the V-band. Both components are rotating faster than synchronously. We
estimate the temperatures and luminosities of the components from the observed
spectral classifications, composite V magnitude, and cluster distance modulus.
The lower limits on the masses derived from the orbital elements and the lack
of eclipses are 25 solar masses and 14 solar masses for the primary and
secondary, respectively. These limits are consistent with the larger masses
estimated from the positions of the stars in the Hertzsprung-Russell diagram
and evolutionary tracks for single stars.
