Intrinsic absorption features in the COS and FUSE spectra of Mrk 509. Normalized relative fluxes are plotted as a function of velocity relative to the systemic redshift of z = 0.034397. The top panel shows the O vi doublet from the FUSE observation in 2000 September with the red side of the doublet as a red line and the blue side of the doublet as a blue line. The middle four panels show the N v, C iv, Si iv and Lyα absorption troughs from our COS observation. The bottom panel shows the Lyγ (red) and Lyβ (black) absorption troughs from the FUSE observation. Dotted vertical lines indicate the velocities of identified absorption components. The thin black vertical line shows v = 0.