The rapidly rotating, hydrogen-deficient, hot post-asymptotic giant branch star ZNG 1 in the globular cluster M5.
DIXON W.V.D., BROWN T.M. and LANDSMAN W.B.
Abstract (from CDS):
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. From the resulting spectrum, we derive an effective temperature Teff= 44300±300 K, a surface gravity logg = 4.3±0.1, a rotational velocity vsini = 170±20 km/s, and a luminosity logL/L☉=3.52±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 of a wind with a terminal velocity near 1000 km/s 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 asymptotic giant branch, but the star's rapid rotation is more easily explained by a previous interaction with a binary companion.
Galaxy: Globular Clusters: Individual: NGC Number: NGC 5904 - Stars: AGB and Post-AGB - Stars: Individual: Alphanumeric: NGC 5904 ZNG 1 - Stars: Mass Loss - Ultraviolet: Stars