Discovery of two bright DO-type white dwarfs

TL;DR

This paper reports the discovery and detailed atmospheric analysis of two bright DO-type white dwarfs, including their temperatures, gravities, and atmospheric compositions, with results consistent with Gaia distance measurements.

Contribution

It presents the identification of two new bright DO white dwarfs and provides their atmospheric parameters using non-LTE models, expanding the known sample of such stars.

Findings

Two bright DO white dwarfs discovered and characterized.

Atmospheric parameters determined with non-LTE models.

Spectroscopic distances agree with Gaia parallaxes.

Abstract

We discovered two bright DO-type white dwarfs, GALEXJ053628.3+544854 (J0536+5448) and GALEX231128.0+292935(J2311+2929), which rank among the eight brightest DO-type white dwarfs known. Our non-LTE model atmosphere analysis reveals effective temperatures and surface gravities of $T_{\mathrm{eff}}=80000\pm4600\,\mathrm{K}$ and $\log \mathrm{g}=8.25\pm0.15$ for J0536+5448 and $T_{\mathrm{eff}}=69400\pm900\,\mathrm{K}$ and $\log \mathrm{g}=7.80\pm0.06$ for J2311+2929. The latter shows a significant amount of carbon in its atmosphere ($C=0.003^{+0.005}_{-0.002}$, by mass), while for J0536+5448 we could derive only an upper limit of $C<0.003$. Furthermore, we calculated spectroscopic distances for the two stars and found a good agreement with the distances derived from the Gaia parallaxes.