The Egg Nebula (CRL 2688)

This is a thirty-second exposure taken on the night of September 22nd 1994 (UT of observation 23/09/94:05:42). This photograph shows a region 50 arc seconds square. The first image has been compressed in brightness and very carefully windowed to try to show the amazing structure in this object. With some image viewers on certain computers, you may need to lighten the picture to see everything that's there. The second image is a pseudo-color version of the same original, in a different attempt to reveal its oddities. Observing conditions were not as good as the telescope optics, so that this image has a "seeing" measurement (average FWHM of several stars) of about 0.9 arc seconds. Orientation: N up with W to the left. 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: 21 02 18 +36 41 34 (2000.0), size: about 25 arc seconds (very roughly 0.4 light-years) across.