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W. V. Dixon (JHU), T. M. Brown (STScI), J. C. Howk (UCSD), W. B. Landsman (SSAI)
FUSE and HST/STIS observations of the UV-bright star ZNG 1 in the globular cluster M5 (NGC 5904) reveal it to be a helium-rich, post-asymptotic giant branch (PAGB) star enhanced in carbon, nitrogen, and oxygen, with a high rotational velocity (170 km/s) and a fast stellar wind (1000 km/s). Its spectrum exhibits high-velocity absorption by both neutral and high-ionization (O VI, C IV, and Si IV) species. Blue-shifted by approximately 180 km/s relative to the stellar photosphere and by 100 to 150 km/s relative to the LSR, the absorption represents either circumstellar material (e.g., gas ejected during the star's AGB phase and now shock-heated by the fast PAGB wind) or a high-ionization high-velocity cloud (HVC) along the line of sight to M5. If the latter, it would be the first evidence that highly-ionized HVCs may be found near the Galactic disk. In this poster, we use these data to improve previous estimates of the stellar parameters and test the possibility that the star is a merger remnant; to determine the star's iron abundance and compare it to the cluster mean; and to investigate the origin of the blue-shifted absorption.
This work is supported by NASA grant NNG04GC44G6.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.