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T.M. Brown, H.C. Ferguson (Space Telescope Science Institute), R.W. O'Connell (University of Virginia), R.G. Ohl (NASA/GSFC)
We present far-UV spectroscopy of the giant elliptical galaxy NGC1399, obtained with the Far Ultraviolet Spectroscopic Explorer. Of all quiescent ellipticals with measured UV emission, NGC1399 has the strongest known ``UV upturn'' - a sharp rise in the spectrum shortward of 2500 Å. It is now well-established that this emission comes from hot horizontal branch (HB) stars and their progeny; however, the chemical composition of these stars has been the subject of a long-standing debate. Our spectra, covering 900 - 1200 Å, clearly show photospheric absorption lines from the hot HB stars in this galaxy. The abundance of N appears nearly solar, Si is at 30% of the solar value, and C is at 4% of the solar value. Such abundances anomalies are a natural consequence of gravitational diffusion, and are also observed in subdwarf B stars of the Galactic field. Our spectra suggest that the hot stars responsible for the UV upturn are drawn from a metal-rich population.
Although NGC1399 is at the center of the Fornax cluster, we find no evidence for OVI cooling flow emission. The upper limit to \lambda\lambda 1032,1038 emission is 3.6 \times 10-15 erg s-1 cm-2, equivalent to 0.1 M\odot yr-1. This OVI emission is far less than that predicted by cooling flow models of the observed NGC1399 X-ray luminosity.