  Massive and luminous O-star atmospheres with winds have been studied
primarily using one-dimensional (1D), spherically symmetric, and stationary
models. However, observations and theory rather suggest that O-star atmospheres
are highly structured, turbulent, and time-dependent. As such, when comparing
to observations, present-day 1D modeling tools need to introduce ad-hoc
quantities such as photospheric macro & microturbulence, wind clumping, etc. We
present multi-dimensional, time-dependent, radiation-hydrodynamical (RHD)
simulations for O-stars that encapsulate the deeper sub-surface envelope (down
to T ~ 450 kK) as well as the supersonic line-driven wind outflow in one
unified approach. Time-dependent, two-dimensional (2D) simulations of O-star
atmospheres with winds are performed using a flux-limiting RHD finite volume
modeling technique. Opacities are computed using a hybrid approach combining
tabulated Rosseland means with calculations (based on the Sobolev
approximation) of the enhanced line opacities expected for supersonic flows.
When compared to 1D models, the average structures in the 2D simulations
display less envelope expansion, no sharp density-inversions, density and
temperature profiles that are significantly less steep around the photosphere,
and a strong anti-correlation between velocity and density in the supersonic
wind. To qualitatively match the different density and temperature profiles
seen in our multi-D and 1D models, we need to add a modest amount of convective
energy transport in the deep sub-surface layers and a large turbulent pressure
around the photosphere to the 1D models.
