Radiation Induced Warping of Protostellar Accretion Disks

We examine the consequences of radiatively driven warping of accretion disks surrounding pre-main-sequence stars. These disks are stable against warping if the luminosity arises from a steady accretion flow, but are unstable at late times when the intrinsic luminosity of the star overwhelms that provided by the disk. Warps can be excited for stars with luminosities of around 10L⊙ or greater, with larger and more severe warps in the more luminous systems. A twisted inner disk may lead to high extinction towards stars often viewed through their disks. After the disk at all radii becomes optically thin, the warp decays gradually on the local viscous timescale, which is likely to be long. We suggest that radiation induced warping may account for the origin of the warped dust disk seen in Beta Pictoris, if the star is only ∼ 10 − 20 Myr old, and could lead to non-coplanar planetary systems around higher mass stars. ApJ Letters, in press Subject headings: accretion, accretion disks — instabilities — circumstellar matter — stars: individual (β Pictoris) — planetary systems — stars: pre-main-sequence