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Session 53 - SNs, Planetaries and Circumstellar Disks.
Display session, Wednesday, June 10
Atlas Ballroom,
We report the discovery of a circumstellar disk around the young A0 star, HR 4796, in thermal infrared images obtained at the Keck telescope. The disk appears nearly edge on at \lambda = 20.8\mum, with diameter \sim3'' (corresponding to R\sim200 AU at the 67 pc distance of HR 4796) and long axis at PA \sim 30^\circ. The intensity of emission does not decrease monotonically with radius but increases outward from the star and peaks near both edges. This appearance accords well with previous interpretations of the spectral energy distribution from which the presence of a solar-system-sized hole in the disk is inferred, perhaps cleared out by processes associated with planet formation. We refine estimates of the size of the hole with the aid of simulated images generated by a simple model of the disk emission and confirm its size as being very similar to that of the region enclosed by the inner edge of our own Kuiper belt. With an age of 10 Myr, HR 4796 may possess a disk in a transitional planet-forming stage between that of a truly proto-planetary disk, as perhaps exemplified by the molecular gas around the Herbig Ae star MWC 480, and more tenuous debris disks like that detected around the much older (100 Myr) A0 star, Vega.
