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F. Menard (CFHT), K. Stapelfeldt (JPL/Caltech), J. Krist (STScI), G. Duvert (Obs. de Grenoble), D. Padgett (IPAC/Caltech), C. Burrows (STScI)
UY Aurigae is a 0.9\prime\prime (125 AU) low-mass pre-main sequence binary with a circumbinary CO disk detected via millimeter interferometry by Duvert et al. 1998. The rotation curve of the gas is compatible with Keplerian motion. Near-infrared adaptive optics images by Close et al. 1998 discovered a patchy reflection nebulosity overlapping the near side of the CO disk, and which they interpreted as an arc segment of the disk rendered visible by enhanced forward scattering due to small dust grains. The system's inclination is estimated to be 42o. We have obtained the first visible wavelength images of UY Aur using the WFPC2 camera on the Hubble Space Telescope and PUEO, the Adaptive Optics system of the Canada-France-Hawaii Telescope. The HST images bring the circumbinary nebula into sharper definition than previously seen, and seem to require a more complex structure than the simple circumbinary disk modeled by Close et al. Two separate and overlapping components are seen in the nebula. One is southeast of the binary and appears broadly conical. The other is a thin, elongated wisp running across the first component, curving around the west side of the binary, and disappearing off toward the north. Across the wavelength coverage of the HST and AO images (RIJHK), the southwest (near) side of the disk appears brighter at shorter wavelength with respect to the stars. On the northeast side of the binary, there is no evidence for optical nebulosity that would correspond to the backscattering (far) side of the proposed circumbinary ring, to a limiting surface brightness 3 mag fainter than the peak nebular brightness southwest of the stars. In the disk model, either a very strongly forward-throwing scattering phase function for the dust or a larger AV toward the back side of the disk is required.
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