The Angular Expansion and Distance of the Planetary Nebula BD+30 3639 (2002)
Li, Jianyang, Harrington, J. Patrick, Borkowski, Kazimierz J.
The WFPC2 camera aboard the HST was used to obtain images of the planetary nebula BD+30 3639 at two epochs separated by 5.663 years. The expansion of the nebula in the H-alpha and [N II] bands has...