Discovery of two bright DO-type white dwarfs

Abstract

We discovered two bright DO-type white dwarfs, GALEX J053628.3+544854 (J0536+5448) and GALEX J231128.0+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_eff} = 80000± 4600 K and log g = 8.25± 0.15 for J0536+5448 and {T_eff} = 69400± 900 K and log g = 7.80± 0.06 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.