Proper‐Motion Measurements of the Cygnus Egg Nebula

We present the results of proper-motion measurements of the dust shellstructure in the Egg Nebula (AFGL 2688, CRL 2688, V1610 Cyg), based on thearchived two-epoch imaging-polarimetry data in the 2 micron band taken withNICMOS on-board the Hubble Space Telescope. We measured the amount of motionsof local structures in the nebula by determining their relative shifts over aninterval of 5.5 years. The dynamical age of the nebula is found to be roughly350 years based on the overall motion of the nebula that exhibits aHubble-law-esque linear relation between the measured proper motion and theprojected radial distance from the origin of the expansion. By adopting thede-projected velocity of 45 km/s at the tips of the bipolar lobes, ourproper-motion measurements indicate that the distance to the Egg Nebula isabout 420 pc and that the lobes are inclined at 7.7 degrees with respect to theplane of the sky. The refined distance estimate yields the luminosity of thecentral star of 3.3 x 10^3 L_sun, the total shell mass of 1.2 M_sun, and themass loss rate (the upper limit) of 3.6 x 10^(-3) M_sun/yr. Assuming 0.6 M_suncentral post-AGB stellar mass, the initial mass of the Egg is 1.8 M_sun. Uponanalysis, we also discovered that the central star of the Egg Nebula has propermotion of its own at the rate of (14, -10) mas/yr.Comment: To appear in ApJ in April 2006. 11 ApJ emulated pages including 2 tables and 4 figure