Published in Astronomy Magazine, March, 2011, page 70
MWP1 (Motch, Werner Pakull), PNG 80.8-10.6, is an ancient, bipolar planetary nebula located at RA 21hr 19m and DEC +34deg 24min in Cygnus with a distance of 1400 light years. MWP1 is one of the largest known PNe. It has an apparent size of 13’x 9′ and an estimated age of 150,000 years. It is a challenge for scientists studying its evolutionary history because its expansion time of 150 000 years (if an expansion velocity of 20 km/s is assumed) is at least two orders of magnitude longer than the time since the central star’s departure from the AGB (about 1000 years). One possible explanation for this discrepancy may be found in the born-again post-AGB nature of the central star: A late He-shell flash at already declining luminosity brings back the star to the AGB and it experiences a second, He-burning, post-AGB phase on a three times longer time scale. However, a “normal” PN will disperse in about 20 000 years below the detection limit and hence, MWP1 has to have extraordinary parameters. ASTRONOMY & ASTROPHYSICS MARCH II 1999, PAGE 487. It is also rare, being a bipolar nebula, in which accounts for about 10% of young PNe. It is also interacting with the interstellar medium. A bipolar structure may suggest that there is a close binary central star or one that has a significant magnetic field. The central star, RX J2117.1+3412, is also a pulsating GW Vir star. (Tweedy, RW and Kwitter KB, “An Atlas of Ancient Planetary Nebula and Their Interaction with the Interstellar Medium” J. Astrophys. Supp. V107, p 2556 (1996).