Bispectrum speckle interferometry of the Red Rectangle:
diffraction-limited near-infrared images reconstructed
from Keck telescope speckle data
P.G. Tuthill, A.B. Men'shchikov, D. Schertl, J.D. Monnier,
W.C. Danchi, and G. Weigelt
Astronomy & Astrophysics 389, 889 (2002)
Abstract.
We present new near-infrared (2.1-3.3µm) 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 1 arcmin and from the visible
(red) to at least 10 mic, 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 0.6-0.8µm
(Osterbart et al. 1997) and 0.7-2.2µm
(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 flat 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
>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.