The structure of the prototype bipolar protoplanetary nebula CRL 2688 (Egg Nebula):: Broadband, polarimetric, and H2 line imaging with NICMOS on the Hubble Space Telescope

High-resolution near-infrared (1.65-2.1 mu m) images and 2 mu m polarimetric images of the inner 19".5 x 19".3 region of the bipolar protoplanetary nebula CRL 2688, taken with the newly installed Near-Infrared Camera and Multiobject Spectrometer (NICMOS) aboard the Hubble Space Telescope (HST), are reported. The NICMOS images reveal a wealth of structure also seen in HST Wide Field Planetary Camera 2 images but not detected in previous, ground-based near-infrared imaging studies. In particular, we detect a system of concentric arcs centered on, and twin "searchlight beams" emanating from, the obscured central star. The images also show two sharply bounded spindle-shaped polar cavities with point-symmetric structure, and the 2.122 mu m H-2 S(1) upsilon = 1-0 emission-line image clearly resolves the sharp interface between the high-velocity outflow that produces these polar cavities and the surrounding slow outflow that forms the extended nebula. The H-2 image also resolves the bright equatorial H, emission into distinct components and elucidates their detailed morphologies. We have discovered, within the dark lane that bifurcates the bipolar lobes of CRL 2688, a compact source of unpolarized light. Our imaging polarimetry shows that this source is not the post-asymptotic giant branch star that illuminates the nebula; we conclude that the compact source is a companion star.