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G. M. Williger (Johns Hopkins U.), C. A. Grady (Eureka Scientific and NASA/GSFC), B. E. Woodgate (NASA/GSFC), J.-C. Bouret (Obs. Marseille-Provence), A. Roberge (Dept. Terr. Magnetism, CIW), M. Sahu (Catholic U. and NASA/GSFC)
Far Ultraviolet Spectroscopic Explorer (FUSE) far-UV (FUV) spectra provide an unique view of accretion and stellar activity in nearby, minimally reddened pre-main sequence stars. We present first results of the FUSE Legacy study of young, intermediate-mass stars. The FUSE data show that over 1--10 Myr, Herbig Ae stars closely resemble classical T Tauri stars by having FUV excess light and a rich emission-line spectrum. The line profile shapes are distinctive and include double-peaked C III 1176 A profiles. The blue emission component in C III 1176 is at the jet footprint velocity in the two FUSE Herbig Ae stars with known microjets. These stars also have O III] and Si III] emission in Space Telescope Imaging Spectrograph and archival International Ultraviolet Explorer data. We report the presence of similar emission profiles in MWC 480 and AB Aur, suggesting that these stars are both driving microjets. The majority of the Herbig Ae stars with FUSE data have O VI surface fluxes in a narrow range. Non-accreting, co-eval A stars, mostly with known debris disks, have O VI surface fluxes a factor of 50--100 below the level seen in the accreting systems. The FUSE data permit us to identify several transitional systems with low or no detectable FUV excesses, and with infrared spectral energy distributions suggesting central clearing with cavities as large as r=10 AU, which may be due to dynamical clearing by planets. The scarcity of stars with activity levels intermediate between the Herbig Ae stars and the debris disks suggests that activity drops rapidly with the end of accretion, in contrast to solar-type stars, but persists to at least the age of Beta Pictoris at 12 Myr. This study uses data obtained under FUSE programs C126, D065, and E510, as well as archival FUSE data and HST data from HST-GTO-8801 and 8065.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.