Variable O VI and N V Emission from the X-ray Binary LMC X-3: Heating of
  the Black Hole Companion
  Based on high-resolution ultraviolet spectroscopy obtained with FUSE and COS,
we present new detections of O VI and N V emission from the black-hole X-ray
binary (XRB) system LMC X-3. We also update the ephemeris of the XRB using
recent radial velocity measurements obtained with the echelle spectrograph on
the Magellan-Clay telescope. We observe significant velocity variability of the
UV emission, and we find that the O VI and N V emission velocities follow the
optical velocity curve of the XRB. Moreover, the O VI and N V intensities
regularly decrease between binary phase = 0.5 and 1.0, which suggests that the
source of the UV emission is increasingly occulted as the B star in the XRB
moves from superior to inferior conjunction. These trends suggest that
illumination of the B-star atmosphere by the intense X-ray emission from the
accreting black hole creates a hot spot on one side of the B star, and this hot
spot is the origin of the O VI and N V emission. However, the velocity
semiamplitude of the ultraviolet emission, K_{UV}~180 km/s, is lower than the
optical semiamplitude; this difference could be due to rotation of the B star.
If our hypothesis about the origin of the highly ionized emission is correct,
then careful analysis of the emission occultation could, in principle,
constrain the inclination of the XRB and the mass of the black hole.
