The Disk and Environment of the Herbig B[CLC]e[/CLC] Star HD 100546

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Abstract
Coronagraphic imaging of the nearest Herbig Be star with the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope, Ks (2.15 μm) imaging with ADONIS at the 3.6 m telescope at La Silla, and mid-infrared imaging with OSCIR using the 4 m Blanco Telescope at Cerro Tololo Inter-American Observatory confirm the detection of the disk reported by Pantin et al. and map the disk out to 5'' (~515 AU) in the optical and at Ks. While the source is unresolved at 10 and 18 μm, it can be traced to 15 at 11.7 μm. We confirm the change in the radial dependence of the disk surface brightness near 27 seen at 1.6 μm by Augereau et al. at Ks. No such break in the power law is seen in the optical. The STIS data reveal spiral dark lane structure, making HD 100546 the third near–zero-age main-sequence Herbig Ae/Be star with structure more than 100 AU from the star. We also optically detect a low surface brightness envelope extending 10'' (1000 AU) from the star, in addition to nebulosity, which is probably associated with DC 292.6-7.9. The survival of the envelope through essentially the entire pre–main-sequence lifetime of the star, coupled with the absence of physical companions within 1500 AU of the star, suggests that envelope lifetimes owe more to the star-forming environment than to mass-loss activity from the Herbig Ae/Be star.