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

TL;DR

This study provides the most comprehensive UV spectroscopic analysis of the hot DA white dwarf G191-B2B, identifying thousands of absorption features, updating elemental abundances, and revealing potential circumstellar material.

Contribution

It offers the first detailed NLTE abundance measurement for aluminum and the most complete UV spectral survey of any white dwarf to date.

Findings

Identified 947 absorption lines, mainly from Fe and Ni.

Detected potential circumstellar Si III material.

Updated elemental abundances, including first NLTE Al measurement.

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 \textit{HST} STIS E140H, E230H, and \textit{FUSE} observations, covering the spectral ranges of 1150-3145\AA\, and 910-1185\AA\, 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 m\AA. In total, 976 absorption features have been detected to $3\sigma$ 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 \textit{FUSE} spectrum have now been identified, and relatively few remain elusive in the STIS spectrum.