The UV-Bright Stars of Omega Centauri

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Session 12 -- Stars and Variable Stars
Oral presentation, Monday, June 12, 1995, 10:00am - 11:30am

[12.03] The UV-Bright Stars of Omega Centauri

W.B.Landsman (HSTX/GSFC/LASP), A.Crotts (Columbia Univ.), R.W.O'Connell, J.H.Whitney (UVa), T.Lanz (USRA/GSFC/LASP), T.P.Stecher (NASA/GSFC/LASP)

Images of the globular cluster Omega Centauri obtained with the Ultraviolet Imaging Telescope (UIT) in 1990 revealed numerous hot stars more luminous than zero-age horizontal branch (Whitney et al.\ 1994, AJ, 108, 1350). We have obtained CTIO 4m and IUE low-dispersion spectra of seven of the brightest stars in the Whitney et al.\ catalog. The target stars include UIT-1 and UIT-2 in the core of Omega Cen (Landsman et al. 1992 ApJL, 395, L21), as well as ROA 5342, Dk 3873, and Dk 3089 from the catalog of Dickens (1988).

All of the target stars are found to be radial velocity members of the cluster. Three of the stars (ROA 5342, UIT-151, Dk 3873) show strong He II lines in their spectra and are probably very hot ($>$ 50,000 K) post-AGB stars. The remaining four stars show strong He I lines, and UIT-1 also shows numerous nitrogen lines. We present results of an atmospheric analysis to constrain the reddening, effective temperatures, and helium abundances.

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