WeBo 1

WeBo 1 is a very unusual young planetary nebula between the Heart (IC 1805) and Soul (W5) nebulas in Cassiopeia. Two things make it unusual. First is its shape. Rather than being globular or spherical in shape, it presents as a thin ellipse. This is likely due to the fact that its progenitor star (not visible in the frame) is part of a binary system, and the gravitational interaction with its companion star caused material to be ejected from the system in a disk shape. Second, the binary companion (visible at the center of the nebula) is what scientists call a barium star. Barium stars are fairly rare.

Ronald F. Webbink discovered WeBo 1 looking a sky-survey data in 1995 and his colleague Howard E. Bond took narrowband CCD images of it to determine more about its nature. In their 2003 paper on WeBo 1 co-authored with Don L. Pollacco, they posit that the progenitor white dwarf star was once an asymptotic giant branch (AGB) star.

A star in its brief AGB stage has burned through all its hydrogen and has begun fusing heavier elements, which causes it to expand dramatically and start shedding its outer layers. These outer layers can contain newly synthesized heavier elements. In this case, the large binary companion star accreted some of this heavy-element material, which contaminated its atmosphere.

Bond, Pollacco, and Webbink estimate WeBo 1’s distance at around 5,000 light years from earth and its age between 6,000 and 18,000 years. They also were able to cite only one other planetary nebula (SuWt 2 in the southern hemisphere) with a similar flat, elliptical shape.