We report observations of the hot post-asymptotic giant branch star ZNG 1 in the globular cluster M5 ( NGC 5904 ) with the Far Ultraviolet Spectroscopic Explorer ( FUSE ) .
From the resulting spectrum , we derive an effective temperature T _ { eff } = 44300 \pm 300 K , a surface gravity \log g = 4.3 \pm 0.1 , a rotational velocity v \sin i = 170 \pm 20 km s ^ { -1 } , and a luminosity \log L / L _ { \sun } = 3.52 \pm 0.04 .
The atmosphere is helium-rich ( Y = 0.93 ) , with enhanced carbon ( 2.6 % by mass ) , nitrogen ( 0.51 % ) and oxygen ( 0.37 % ) abundances .
The spectrum shows evidence for a wind with terminal velocity near 1000 km s ^ { -1 } and an expanding shell of carbon- and nitrogen-rich material around the star .
The abundance pattern of ZNG 1 is suggestive of the “ born-again ” scenario , whereby a star on the white-dwarf cooling curve undergoes a very late shell flash and returns to the AGB , but the star ’ s rapid rotation is more easily explained by a previous interaction with a binary companion .