NICMOS Imaging of the HR 4796A Circumstellar Disk

Abstract

We report the first near-infrared (NIR) imaging of a circumstellar annular disk around the young (#8 Myr), Vega-like star HR 4796A. NICMOS coronagraph observations at 1.1 and 1.6 mm reveal a ringlike symmetrical structure that peaks in reflected intensity (#70 AU) from the central A0 V star. The ring geometry, 1#.05 # 0#.02 with an inclination of and a major axis position angle of , is in good agreement with 73#.1 # 1#.2 26#.8 # 0#.6 recent 12.5 and 20.8 mm observations of a truncated disk. The ring is resolved with a characteristic width of less than 0#.26 (17 AU) and appears abruptly truncated at both the inner and outer edges. The region of the diskplane inward of #60 AU appears to be relatively free of scattering material. The integrated flux density of the part of the disk that is visible (greater than 0#.65 from the star) is found to be and mJy at 7.6 # 0.5 7.4 # 1.2 1.1 and 1.6 mm, respectively. Correcting for the unseen area of the ring yields total flux densities of ...