Far Ultraviolet Spectroscopic Explorer ( FUSE ) spectra of 22 Galactic halo stars are studied to determine the amount of O vi in the Galactic halo between \sim 0.3 and \sim 10 kpc from the Galactic mid-plane .
Strong O vi \lambda 1031.93 absorption was detected toward 21 stars , and a reliable 3 \sigma upper limit was obtained toward HD 97991 .
The weaker member of the O vi doublet at 1037.62 Å could be studied toward only six stars because of stellar and interstellar blending problems .
The measured logarithmic total column densities vary from 13.65 to 14.57 with < log N > = 14.17 \pm 0.28 ( 1 \sigma ) .
The observed columns are reasonably consistent with a patchy exponential O vi distribution with a mid-plane density of 1.7 \times 10 ^ { -8 } cm ^ { -3 } and scale height between 2.3 and 4 kpc .
We do not see clear signs of strong high-velocity components in O vi absorption along the Galactic sight lines , which indicates the general absence of high velocity O vi within 2-5 kpc of the Galactic mid-plane .
This result is in marked contrast to the findings of Sembach et al .
who reported high velocity O vi absorption toward \sim 60 % of the complete halo sight lines observed by FUSE .
The line centroid velocities of the O vi absorption does not reflect Galactic rotation well .
The O vi velocity dispersions range from 33 to 78 km s ^ { -1 } with an average of < b > = 45 \pm 11 km s ^ { -1 } ( 1 \sigma ) .
These values are much higher than the value of \sim 18 km s ^ { -1 } expected from thermal broadening for gas at T \sim 3 \times 10 ^ { 5 } K , the temperature at which O vi is expected to reach its peak abundance in collisional ionization equilibrium .
Turbulence , inflow , and outflow must have an effect on the shape of the O vi profiles .
Kinematical comparisons of O vi with Ar i reveal that 8 of 21 sight lines are closely aligned in LSR velocity ( | \Delta V _ { LSR } | \leq 5 km s ^ { -1 } ) , while 9 of 21 exhibit significant velocity differences ( | \Delta V _ { LSR } | \geq 15 km s ^ { -1 } ) .
This dual behavior may indicate the presence of two different types of O vi-bearing environments toward the Galactic sight lines .
The correlation between the H i and O vi intermediate velocity absorption is poor .
We could identify the known H i intermediate velocity components in the Ar i absorption but not in the O vi absorption in most cases .
Comparison of O vi with other highly-ionized species suggests that the high ions are produced primarily by cooling hot gas in the Galactic fountain flow , and that turbulent mixing also has a significant contribution .
The role of turbulent mixing varies from negligible to dominant .
It is most important toward sight lines that sample supernova remnants like Loop I and IV .
The average N ( C iv ) /N ( O vi ) ratios for the nearby halo ( this work ) and complete halo ( Savage et al . )
are similar ( \sim 0.6 ) , but the dispersion is larger in the sample of nearby halo sight lines .
We are able to show that the O vi enhancement toward the Galactic center region that was observed in the FUSE survey of complete halo sight lines ( Savage et al . )
is likely associated with processes occurring near the Galactic center by comparing the observations toward the nearby HD 177566 sight line to those toward extragalactic targets .