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J.E. Krist (STScI), K.R. Stapelfeldt (JPL/Caltech), C.J. Burrows (STScI/ESA), F. Menard (CFHT), D.L. Padgett (IPAC/Caltech)
HST/WFPC2 observations of the isolated T Tauri star TW Hydrae suggest the presence of a face-on circumstellar disk. Subtraction of a reference point spread function (PSF) reveals a smooth, symmetrical, circular halo around the star. This halo is 3" (170 AU) in radius, appears in both our F606W (wide R-band) and F814W (WFPC2 I-band) images, and has also been detected in the near-infrared using HST/NICMOS by the NICMOS science team. Known artifacts in the WFPC2 camera, the effects of telescope breathing, and the effect of normalization errors on the PSF subtraction have all been investigated as possible instrumental origins for the halo. However, none of these accounts for the structure that is seen. The most likely explanation is a circumstellar reflection nebula around TW Hya. The brightness of the halo declines steeply with radius, but includes a ``plateau'' region between 1.5" < r < 2.3". Preliminary modelling of the observed intensity profile and IRAS fluxes indicates that the disk must be moderately optically thick.
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