3D spectroscopic analysis of helium-line white dwarfs

In this paper, we present corrections to the spectroscopic parameters of DB and DBA white dwarfs with -10.0 ≤ log (H/He) ≤ -2.0, 7.5 ≤ log g ≤ 9.0, and $12\, 000$ ≲ T_eff $\lesssim 34\, 000\,\mathrm{ K}$ , based on 282 3D atmospheric models calculated with the CO⁵BOLD radiation-hydrodynamics code. These corrections arise due to a better physical treatment of convective energy transport in 3D models when compared to the previously available 1D model atmospheres. By applying the corrections to an existing Sloan Digital Sky Survey (SDSS) sample of DB and DBA white dwarfs, we find significant corrections both for effective temperature and surface gravity. The 3D log g corrections are most significant for T_eff ≲ 18 000 K, reaching up to -0.20 dex at log g = 8.0. However, in this low effective temperature range, the surface gravity determined from the spectroscopic technique can also be significantly affected by the treatment of the neutral van der Waals line broadening of helium and by non-ideal effects due to the perturbation of helium by neutral atoms. Thus, by removing uncertainties due to 1D convection, our work showcases the need for improved description of microphysics for DB and DBA model atmospheres. Overall, we find that our 3D spectroscopic parameters for the SDSS sample are generally in agreement with Gaia Data Release 2 absolute fluxes within 1σ-3σ for individual white dwarfs. By comparing our results to DA white dwarfs, we determine that the precision and accuracy of DB/DBA atmospheric models are similar. For ease of user application of the correction functions, we provide an example PYTHON code.