Photospheric Abundances of the Hot Stars in NGC 1399
Abstract
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 λ λ 1032,1038 emission is 3.6 x 10-15 erg s-1 cm-2, equivalent to 0.1 Msun yr-1. This OVI emission is far less than that predicted by cooling flow models of the observed NGC1399 X-ray luminosity.
- Publication:
-
American Astronomical Society Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AAS...199.2002B