2001ApJ...551L..97R

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 gases that have a wide range in temperature, from hot O VI emission to cold H₂ 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 that the total column density of H₂ toward AB Aur from the FUSE spectrum is N(H₂)=(6.8±0.5)x10¹⁹ cm^–2. The gas kinetic temperature of the H₂ derived from the ratio N(J=1)/N(J=0) is 65±4 K. The column density of the CO observed in the STIS spectrum is N(CO)=(7.1±0.5)x10¹³ cm^–2, giving a CO/H₂ ratio of (1.04±0.11)x10^–6. We also use the STIS spectrum to find the column density of H I, which permits us to calculate the total column density of hydrogen atoms, the fractional abundance of H₂, and the gas-to-dust ratio.