A photospheric metal line profile analysis of hot DA white dwarfs with circumstellar material

TL;DR

This study investigates how circumstellar material affects the measurement of metal abundances in hot DA white dwarfs, emphasizing the need for models that incorporate both circumstellar and photospheric line profiles.

Contribution

It introduces a method that accounts for physical line profiles of circumstellar and photospheric features, improving abundance estimates in white dwarf spectra.

Findings

Circumstellar contamination can significantly alter photospheric metal abundance estimates.

Including circumstellar line profiles reduces the derived C and Si abundances in five of six studied stars.

Previous models were insufficient to reproduce observed line profiles, highlighting the need for improved techniques.

Abstract

Some hot DA white dwarfs have circumstellar high ion absorption features in their spectra, in addition to those originating in the photosphere. In many cases, the line profiles of these absorbing components are unresolved. Given the importance of the atmospheric composition of white dwarfs to studies of stellar evolution, extra-solar planetary systems and the interstellar medium, we examine the effect of including circumstellar line profiles in the abundance estimates of photospheric metals in six DA stars. The photospheric C and Si abundances are reduced in five cases where the circumstellar contamination is strong, though the relative weakness of the circumstellar Si IV absorption introduces minimal contamination, resulting in a small change in abundance. The inability of previous, approximate models to reproduce the photospheric line profiles here demonstrates the need for a technique that accounts for the physical line profiles of both the circumstellar and photospheric lines when modelling these blended absorption features.