Photospheric Abundances of the Hot Stars in NGC 1399 and Limits on the Fornax Cluster Cooling Flow

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Abstract
We present far-UV spectroscopy of the giant elliptical galaxy NGC 1399, obtained with the Far Ultraviolet Spectroscopic Explorer. Of all quiescent ellipticals, NGC 1399 has the strongest known "UV upturn"—a sharp spectral rise shortward of 2500 Å. It is now well established that this emission comes from hot horizontal branch stars and their progeny; however, the chemical composition of these stars has been the subject of a longstanding debate. For the first time in observations of any elliptical galaxy, our spectra clearly show photospheric metallic absorption lines within the UV upturn. The abundance of N is at 45% solar, Si is at 13% solar, and C is at 2% solar. Such abundance anomalies are a natural consequence of gravitational diffusion. These photospheric abundances fall in the range observed for subdwarf B stars of the Galactic field. Although NGC 1399 is at the center of the Fornax Cluster, we find no evidence for O VI cooling flow emission. The upper limit to λλ1032, 1038 emission is 3.9 × 10-15 ergs s-1 cm-2, equivalent to 0.14 M☉ yr-1 and less than the value predicted by simple cooling flow models of the NGC 1399 X-ray luminosity.