Bispectrum speckle interferometry of the Red Rectangle: Diffraction-limited near-infrared images reconstructed from Keck telescope speckle data

We present new near-infrared (2.1-3.3 mum) images of the Red Rectangle with unprecedented diffraction-limited angular resolutions of 46-68 mas; 4 times higher than that of the Hubble space telescope and almost a factor of two improvement over the previous 6 m SAO telecope speckle images presented by Men'shchikov et al. (1998). The new images, which were reconstructed from Keck telescope speckle data using the bispectrum speckle interferometry method, clearly show two bright lobes above and below the optically thick dark lane obscuring the central binary. X-shaped spikes, thought to trace the surface of a biconical flow, change the intensity distribution of the bright lobes, making them appear broadened or with an east-west double-peak in images with the highest resolution. The striking biconical appearance of the Red Rectangle is preserved on scales from 50 mas to 10 and from the visible (red) to at least 10 mum, implying that large grains of at least several microns in size dominate scattering. The new images supplement previous 76 mas resolution speckle reconstructions at shorter wavelengths of 0.6-0.8 mum (Osterbart et al. 1997) and 0.7-2.2 mum (Men'shchikov et al. 1998), allowing a more detailed analysis of the famous bipolar nebula. The intensity distribution of the images is inconsistent with a at disk geometry frequently used to model the bipolar nebulae. Instead, a geometrically thick torus-like density distribution with bipolar conical cavities is preferred. The extent of the bright lobes indicates that the dense torus has a diameter of greater than or similar to 100 AU, for an assumed distance of 330 pc. This torus may be the outer reaches of a flared thick disk tapering inwards to the central star, however such a density enhancement on the midplane is not strictly required to explain the narrow dark lane obscuring the central stars.