Abell 63

Abell 63 is a planetary nebula in the northern constellation Sagitta whose central star is the eclipsing binary system UU Sagittae (UU Sge). The binary consists of a hot O-type subdwarf primary and a heated M-type main-sequence secondary, with an orbital period of 11.2 hours. The nebula appears as a hollow tube with a hyperbolic waist, a bright central rim, faint end caps, and a surrounding faint circular shell. The system is notable for being both a close detached eclipsing binary and the progenitor of its surrounding planetary nebula.