The Rapidly Rotating, Hydrogen-deficient, Hot Post-Asymptotic Giant Branch Star ZNG 1 in the Globular Cluster M5
Abstract
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-1, and a luminosity log(L/Lsolar)=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-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 asymptotic giant branch, but the star's rapid rotation is more easily explained by a previous interaction with a binary companion.
Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer, which is operated for NASA by Johns Hopkins University under NASA contract NAS5-32985.- Publication:
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The Astrophysical Journal
- Pub Date:
- January 2004
- DOI:
- 10.1086/381389
- arXiv:
- arXiv:astro-ph/0311399
- Bibcode:
- 2004ApJ...600L..43D
- Keywords:
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- 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;
- Astrophysics
- E-Print:
- 8 pages, 2 PostScript figures, Latex with emulateapj5. Accepted for publication in ApJ Letters