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W.B. Landsman (Raytheon), M. Catelan (UVA), F. Grundahl (Aahrus), T. Lanz (UMd/GSFC), C. Proffitt (CSC/STScI), A.V. Sweigart. (GSFC)
We have obtained STIS ultraviolet low-resolution spectra (1140 -- 3100 Å) of eight hot horizontal branch (HB) stars with 10,500 < Teff (K) < 20,000 in the globular cluster NGC 6752 ([Fe/H = -1.6). The two coolest targets have temperatures just coolward of Teff ~ 11,500 K, where a sudden jump in the iron abundance has been observed in optical spectra of HB stars in NGC 6752 (Moehler et al.\ 2000, A&A, 360, 120) presumably due to the onset of radiative levitation. The spectra of the remaining six targets are consistent with an iron abundance near solar. Because this dramatic increase in the iron abundance appears to be characteristic of the HB in all globular clusters (Grundahl et al.\ 1999, ApJ, 524, 242), our data set can be used as a template for the ultraviolet spectral synthesis of the HB of metal-poor populations. An unexpected result is the apparent detection of the 1485 Å\ autoionizing feature of Si II in four of the iron-rich stars.