We present a survey of diffuse O vi emission in the interstellar medium obtained with the Far Ultraviolet Spectroscopic Explorer ( FUSE ) . Spanning 5.5 years of FUSE observations , from launch through 2004 December , our data set consists of 2925 exposures along 183 sight lines , including all of those with previously-published O vi detections .
The data were processed using an implementation of CalFUSE v3.1 modified to optimize the signal-to-noise ratio and velocity scale of spectra from an aperture-filling source .
Of our 183 sight lines , 73 show O vi \lambda 1032 emission , 29 at > 3 \sigma significance .
Six of the 3 \sigma features have velocities |v _ { LSR } | > 120 km s ^ { -1 } , while the others have |v _ { LSR } | < 50 km s ^ { -1 } .
Measured intensities range from 1800 to 9100 LU , with a median of 3300 LU .
Combining our results with published O vi absorption data , we find that an O vi-bearing interface in the local ISM yields an electron density n _ { e } = 0.2–0.3 cm ^ { -3 } and a path length of 0.1 pc , while O vi-emitting regions associated with high-velocity clouds in the Galactic halo have densities an order of magnitude lower and path lengths two orders of magnitude longer .
Though the O vi intensities along these sight lines are similar , the emission is produced by gas with very different properties .