THE STRUCTURE OF THE PROTOTYPE BIPOLAR PROTOPLANETARY NEBULA CRL-2688(EGG NEBULA) - BROAD-BAND, POLARIMETRIC, AND H-2 LINE IMAGING WITH NICMOS ON THE HUBBLE-SPACE-TELESCOPE
R. Sahai et al., THE STRUCTURE OF THE PROTOTYPE BIPOLAR PROTOPLANETARY NEBULA CRL-2688(EGG NEBULA) - BROAD-BAND, POLARIMETRIC, AND H-2 LINE IMAGING WITH NICMOS ON THE HUBBLE-SPACE-TELESCOPE, The Astrophysical journal, 492(2), 1998, pp. 163
High-resolution near-infrared (1.65-2.1 mu m) images and 2 mu m polari
metric images of the inner 19''.5 x 19''.3 region of the bipolar proto
planetary nebula CRL 2688, taken with the newly installed Near-Infrare
d Camera and Multiobject Spectrometer (NICMOS) aboard the Hubble Space
Telescope (HST), are reported. The NICMOS images reveal a wealth of s
tructure 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 twi
n ''searchlight beams'' emanating from, the obscured central star. The
images also show two sharply bounded spindle-shaped polar cavities wi
th 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 surr
ounding slow outflow that forms the extended nebula. The H-2 image als
o 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 compac
t 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.