We present the first observations of a Herbig Ae star with a circumstellar disk by the Far Ultraviolet Spectroscopic Explorer ( FUSE ) , as well as a simultaneous observation of the star obtained with the Hubble Space Telescope Space Telescope Imaging Spectrograph ( STIS ) . The spectra of AB Aurigae show emission and absorption features arising from gasses that have a wide range in temperature , from hot O vi emission to cold H _ { 2 } and CO absorption . Emissions from the highly ionized species O vi and C iii present in the FUSE spectrum are redshifted , while absorption features arising from low-ionization species like O i , N i , and Si ii are blueshifted and show characteristic stellar wind line-profiles . We find the total column density of H _ { 2 } toward AB Aur from the FUSE spectrum , N ( H _ { 2 } ) = ( 6.8 \pm 0.5 ) \times 10 ^ { 19 } cm ^ { -2 } . The gas kinetic temperature of the H _ { 2 } derived from the ratio N ( J = 1 ) / N ( J = 0 ) is 65 \pm 4 K. The column density of the CO observed in the STIS spectrum is N ( CO ) = ( 7.1 \pm 0.5 ) \times 10 ^ { 13 } cm ^ { -2 } , giving a CO / H _ { 2 } ratio of ( 1.04 \pm 0.11 ) \times 10 ^ { -6 } . We also use the STIS spectrum to find the column density of H i , permitting us to calculate the total column density of hydrogen atoms , the fractional abundance of H _ { 2 } , and the gas-to-dust ratio .