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C.A. Grady (NOAO/STIS, NASA/GSFC), B. Woodgate, A. Boggess (LASP, NASA/GSFC), F.C. Bruhweiler (Physics Dept., Catholic University of America), M. Clampin (STScI)
STIS GTO broadband (2000-10,000 Angstroms) optical coronographic imaging of the 2-4 Myr old Herbig Ae star, AB Aur, in January 1999 has revealed a circumstellar disk extending more than 800 AU from the star. The circumstellar reflection nebulosity extends well beyond the CO disk imaged by Mannings and Sargent (1997), and is accompanied by more distant reflection nebulosity. The material within 800 AU of the star is non-uniformly illuminated, and is broadly consistent with detection of a flared disk seen at ~70 degrees inclination inferred from the millimeter data. The STIS data do not indicate any central clearing exterior to the 75 AU region occulted by the STIS coronographic wedge, but do show centro-symmetric striations in the reflection nebulosity at larger distances from the star. The disk surrounding AB Aur is substantially brighter within 300 AU of the star than the slightly older HD 163296 disk imaged in 1998 September with the same observing configuration. Comparison of the IR spectral energy distributions of the two stars as seen by the ISO SWS and LWS (van den Ancker et al. 1999) suggests that mid-IR spectra can be used to predict the degree of clearing in the 100-300 AU region. The STIS data, together with NICMOS coronographic observations of somewhat older Ae/Vega-like stars suggests that circumstellar disks around single stars begin to resemble more mature planetary systems at t>4 Myr.
This study was supported by HST STIS GTO funding through support to AURA/NOAO in response to NASA A/O OSSA-4-84 through the Hubble Space Telescope Project at GSFC. Analysis of the HST STIS data was carried out in the Laboratory for Astronomy & Solar Physics, NASA/GSFC.
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