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The extreme luminosities of hot, massive stars drive strong stellar windsthrough UV line-scattering. For OB stars with an orbiting circumstellar disk,we explore the effect of such line-scattering in ablating disk material,initially focusing on the marginally optically thin decretion disks ofclassical Oe and Be stars. For this we apply a multi-dimensionalradiation-hydrodynamics code, assuming optically thin ray tracing for thestellar continuum and a multi-ray Sobolev treatment of the line transfer. Thisaccounts for desaturation of line-absorption by Keplerian shear in the disk,and associated driving by non-radial photons. Results show dense,intermediate-speed surface ablation, consistent with the strong, blue-shiftedabsorption seen in UV wind lines of Be shell stars. The asymptotic ablationrate is typically an order-unity factor times the stellar wind mass loss rate,leading to disk destruction times of order months to years for Be disks,consistent with observations. The much stronger radiative forces of O starsreduce this time to order days, making sustaining a disk difficult, and soproviding a natural explanation for the rarity of Galactic Oe stars.Additionally, the weakened line-driving at lower metallicity implies both areduction in the winds that help spin-down stars from near-critical rotation,and in the ablation of decretion disks, thus providing a natural explanationfor the higher fraction of Classical Be stars, and the presence of Oe stars, inthe Magellanic Clouds. We conclude with a discussion of future extensions tostudy line-driven ablation of denser, optically thick, accretion disks aroundpre-main-sequence massive stars.

Line-driven ablation of circumstellar disks: I. Optically thin decretion disks of classical Oe/Be stars