Chandra grating spectroscopy of three hot white dwarfs

TL;DR

This study uses Chandra grating spectroscopy to analyze the soft X-ray spectra of three hot white dwarfs, providing insights into their atmospheric composition, temperature, and physical processes like gravitational settling and radiative levitation.

Contribution

First detailed high-resolution X-ray spectral analysis of multiple hot white dwarfs, revealing their atmospheric metal content and temperature constraints.

Findings

LB 1919 has significantly lower metallicity than similar DAs.

GD 246 uniquely shows identifiable iron lines in soft X-ray.

Precise temperature measurement of PG1159 constrains the GW Vir instability region.

Abstract

High-resolution soft X-ray spectroscopic observations of single hot white dwarfs are scarce. With the Chandra Low-Energy Transmission Grating, we have observed two white dwarfs, one is of spectral type DA (LB 1919) and the other is a non-DA of spectral type PG1159 (PG 1520+525). The spectra of both stars are analyzed, together with an archival Chandra spectrum of another DA white dwarf (GD 246). The soft X-ray spectra of the two DA white dwarfs are investigated in order to study the effect of gravitational settling and radiative levitation of metals in their photospheres. LB 1919 is of interest because it has a significantly lower metallicity than DAs with otherwise similar atmospheric parameters. GD 246 is the only white dwarf known that shows identifiable individual iron lines in the soft X-ray range. For the PG1159 star, a precise effective temperature determination is performed in order to confine the position of the blue edge of the GW Vir instability region in the HRD. (abridged)