Faint Object Spectrograph Observations of MRK 509: Ultraviolet Absorption Lines Near the Redshift of the Seyfert Galaxy

Ultraviolet spectra of the Seyfert 1 galaxy Mrk 509 have been obtained with the Faint Object Spectrograph on the Hubble Space Telescope. The spectra show strong absorption lines in the cores of the redshifted emission lines of Lyα and C IV λλ1548.2, 1550.8, confirming an earlier detection in IUE high-dispersion spectra, and a new detection of strong N V λλ1238.8, 1242.8 absorption lines, also near the redshift of Mrk 509. There is no evidence for absorption in the lines of Mg II or Si IV at the redshift of Mrk 509. The absorption lines have two components that are at the same velocities as those in the IUE observations obtained - 12 yr earlier: one at the systemic redshift of the host galaxy, as defined by the low-ionization emission lines in the optical, and one at a radial velocity of -390 km s^-1^ relative to the systemic redshift. The equivalent widths and velocities of the absorption lines indicate that they arise from an extended region of highly ionized gas surrounding the nucleus of the host galaxy consisting of two distinct kinematic components.