A Dust Disk Surrounding the Young A Star HR 4796A

We report the codiscovery of the spatially-resolved dust disk of theVega-like star HR 4796A. Images of the thermal dust emission at $\lambda = 18\mu$m show an elongated structure approximately 200 AU in diameter surroundingthe central A0V star. The position angle of the disk, $30^{\circ} \pm10^{\circ}$, is consistent to the position angle of the M companion star,$225^{\circ}$, suggesting that the disk-binary system is being seen nearlyalong its orbital plane. The surface brightness distribution of the disk isconsistent with the presence of an inner disk hole of approximately 50 AUradius, as was originally suggested by Jura et al. on the basis of the infraredspectrum. HR 4796 is a unique system among the Vega-like or $\beta$ Pictorisstars in that the M star companion (a weak-emission T Tauri star) shows thatthe system is relatively young, $\sim 8 \pm 3$ Myr. The inner disk hole mayprovide evidence for coagulation of dust into larger bodies on a timescalesimilar to that suggested for planet formation in the solar system.Comment: 12 pages, 3 PostScript figures, accepted for publication in Astrophysical Journal Letter