  Around 10% of white dwarfs exhibit global magnetic structures with fields
ranging from 1 kG to hundreds of MG. Recently, the first radiation
magnetohydrodynamics simulations of the atmosphere of white dwarfs showed that
convection should be suppressed in their photospheres for magnetic fields with
strengths B $\gtrsim$ 50 kG. These predictions are in agreement with our
knowledge of stellar physics (e.g. energy transfer in strong magnetic field
regions of the solar photosphere), but have yet to be directly confirmed from
white dwarf observations. We obtained COS far-UV spectroscopy of the weakly
magnetic, hydrogen-atmosphere, white dwarf WD2105-820 and of three additional
non-magnetic, convective remnants (all in the $T_{\mathrm{eff}}$ range
9000-11,000 K). We fitted both the COS and the already available optical
spectra with convective and radiative atmospheric models. As expected, we find
that for two of the non-magnetic comparison stars only convective model fits
predict consistent $T_{\mathrm{eff}}$ values from both the optical and the FUV
spectra. In contrast, for WD2105-820 only the best fitting radiative model
produced consistent results.

Solar and Stellar Astrophysics