Based on high-resolution ultraviolet spectroscopy obtained with the Far Ultraviolet Spectroscopic Explorer ( FUSE ) and the Cosmic Origins Spectrograph , 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 } \approx 180 km s ^ { -1 } , is lower than the optical semiamplitude ; this difference could be due to rotation of the B star .
Comparison of the FUSE observations taken in November 2001 and April 2004 shows a significant change in the O vi emission characteristics : in the 2001 data , the O vi region shows both broad and narrow emission features , while in 2004 only the narrow O vi emission is clearly present . Rossi X-ray Timing Explorer data show that the XRB was in a high/soft state in the Nov. 2001 epoch but was in a transitional state in April 2004 , so the shape of the X-ray spectrum might change the properties of the region illuminated on the B star and thus change the broad vs. narrow characteristics of the UV emission .
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 .