Discovery of two bright DO-type white dwarfs

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 $T_{\mathrm{eff}}=80000\pm 4600\mathrm{K}$ and $\log \mathrm{g}=8.25\pm 0.15$ for J0536+5448 and $T_{\mathrm{eff}}=69400\pm 900\mathrm{K}$ and $\log \mathrm{g}=7.80\pm 0.06$ for J2311+2929. The latter shows a significant amount of carbon in its atmosphere ($C=0.003_{-0.002}^{+0.005}$, 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.

7 pages, 4 figures, accepted for publication in MNRAS

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• How an overweight and rapidly rotating PG 1159 star in the Galactic halo challenges evolutionary models