About this object
CRL 2688, also known as the Egg Nebula, is believed to be a proto-planetary
nebula, representing the transition to the comparatively well-studied
planetary nebula phase. It is well established that the progenitors of
planetary nebulae are stars at the tip of the asymptotic giant branch that
are losing mass in a `super-wind' phase. However, only a few objects are
known which can be reliably identified with this transition from star to
planetary, which makes their study very important. This optical image
shows the double-lobed nebula, which is illuminated by the central F5 star
which is hidden from our direct view by a dust torus. This torus appears
as a strong, though small, infrared source with a temperature of 150K.
The optical emission is very strongly polarized, at about 40%, which is
sufficient to be seen by eye with a Polaroid filter and a moderate-sized
telescope. The distance to CRL 2688 is uncertain, but is probably about
3000 light years.
Location: 23 00.3 +36 30 (1950.0), size: about 25 arc seconds (very roughly 0.4 light years) across.