MASS-LOSS FROM PREMAIN-SEQUENCE ACCRETION DISKS .1. THE ACCELERATING WIND OF FU ORIONIS

We present evidence that the wind of the pre-main-sequence object FU Orionis arises from the surface of the luminous accretion disk. A disk wind model calculated assuming radiative equilibrium explains the differential behavior of the observed asymmetric absorption-line profiles. The model predicts that strong lines should be asymmetric and blueshifted, while weak lines should be symmetric and double-peaked due to disk rotation, in agreement with observations. We propose that many blueshifted ''shell'' absorption features are not produced in a true shell of material, but rather form in a differentially expanding wind that is rapidly rotating. The inference of rapid rotation supports the proposal that pre-main-sequence disk winds are rotationally driven. FU Ori may lose substantial amounts of mass over a significant area of the innermost disk (approximately 10 stellar radii), which could have important implications for the structure of jets from young stellar objects. Our results support the suggestion that massive winds originate from rapidly accreting pre-main-sequence accretion disks.