Photospheric Metals in the FUSE Spectrum of the Subdwarf B Star PG0749+658

Abstract

We present an abundance analysis of the far-ultraviolet (905--1187 A) spectrum of the subdwarf B star PG0749+658, obtained by the Far Ultraviolet Spectroscopic Explorer (FUSE). The data have a resolution of about R = lambda / Delta lambda = 12000--15000 (20--25 km/s). We determine C, N, Si, P, S, Cr, Mn, Fe, Co, and Ni abundances, and upper limits on the abundance of Cl and V, using a grid of synthetic spectra based on a LTE stellar atmosphere model. He, C, N, Si, and Cl are depleted by a factor of >~10 with respect to solar, while P, S, and Fe are diminished by less than a factor of 10. We measure a solar abundance of Cr, Mn, and Co and a Ni enhancement of ~0.6 dex. We compare these values to predictions based on radiative levitation theory. The radial velocity of the foreground interstellar material has one dominant component, and coincides with that of the photospheric lines.