A comprehensive near and far ultraviolet spectroscopic study of the hot DA white dwarf G191-B2B

Abstract

We present a detailed spectroscopic analysis of the hot DA white dwarf G191-B2B, using the best signal to noise, high resolution near and far UV spectrum obtained to date. This is constructed from co-added HST STIS E140H, E230H, and FUSE observations, covering the spectral ranges of 1150-3145Å, and 910-1185Å, respectively. With the aid of recently published atomic data, we have been able to identify previously undetected absorption features down to equivalent widths of only a few mÅ. In total, 976 absorption features have been detected to $3σ$ confidence or greater, with 947 of these lines now possessing an identification, the majority of which are attributed to Fe and Ni transitions. In our survey, we have also potentially identified an additional source of circumstellar material originating from Si {\sc iii}. While we confirm the presence of Ge detected by \citet{vennes05a}, we do not detect any other species. Furthermore, we have calculated updated abundances for C, N, O, Si, P, S, Fe, and Ni, while also calculating, for the first time, an NLTE abundance for Al, deriving Al {\sc iii}/H=$1.60_{-0.08}^{+0.07}\times{10}^{-7}$. Our analysis constitutes what is the most complete spectroscopic survey of any white dwarf. All observed absorption features in the FUSE spectrum have now been identified, and relatively few remain elusive in the STIS spectrum.