FUSE and Hubble Space Telescope/STIS Observations of Hot and Cold Gas in the AB Aurigae System
Deleuil, M.; Bouret, J. -C.; Roberge, A.; Feldman, P. D.; Bruhweiler, F. C.; Lecavelier des Etangs, A.; Ferlet, R.; Vidal-Madjar, A.; Boggess, A.; Andre, M.; Grady, C. A.; Woodgate, B.
United States, France
Abstract
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)×1019 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)×1013 cm-2, giving a CO/H2 ratio of (1.04+/-0.11)×10-6. 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.