  During our spectroscopic survey of central stars of faint planetary nebulae
(PNe), we found that the nucleus of Abell 57 exhibits strong nebular emission
lines. Using synthetic narrow-band images, we show that the emission arises
from an unresolved compact emission knot (CEK) coinciding with the hot (90,000
K) central star. Thus Abell 57 belongs to the rare class of "EGB 6-type" PNe,
characterized by dense emission cores. Photometric data show that the nucleus
exhibits a near-IR excess, due to a dusty companion body with the luminosity of
an M0 dwarf but a temperature of ~1800 K. Emission-line analysis reveals that
the CEK is remarkably dense (electron density ~1.6x10**7 cm**-3), and has a
radius of only ~4.5 AU. The CEK suffers considerably more reddening than the
central star, which itself is more reddened than the surrounding PN. These
puzzles may suggest an interaction between the knot and central star; however,
Hubble Space Telescope imaging of EGB 6 itself shows that its CEK lies more
than ~125 AU from the PN nucleus. We discuss a scenario in which a portion of
the AGB wind that created the PN was captured into a dust cloud around a
distant stellar companion; this cloud has survived to the present epoch, and
has an atmosphere photoionized by radiation from the hot central star. However,
in this picture EGB 6-type nuclei should be relatively common, yet they are
actually extremely rare; thus they may arise from a different transitory
phenomenon. We suggest future observations of Abell 57 that may help unravel
its mysteries.
