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We propose that FU Orionis outbursts may play an important role inmaintaining the slow rotation of classical disk-accreting T Tauri stars.Current estimates for the frequency and duration of FU Orionis outbursts andthe mass accretion rates of T Tauri and FU Orionis stars suggest that more massmay be accreted during the outbursts than during the T Tauri phases. If this isthe case, then the outbursts should also dominate the accretion of angularmomentum. During the outbursts, the accretion rate is so high that the magneticfield of the star should not disrupt the disk, and the disk will extend all theway in to the stellar surface. Standard thin disk models then predict that thestar should accrete large amounts of angular momentum, which will produce asecular spinup of the star. We present boundary layer solutions for FU Orionisparameters which show that the angular momentum accretion rate drops below zerofor stellar rotation rates which are always substantially below breakup, butdepend on the mass accretion rate and on the adopted definition of the stellarradius. When the angular momentum accretion rate drops close to zero, the starwill stop spinning up. Faster stellar rotation rates will produce negativeangular momentum accretion which will spin the star down. Therefore, FU Orionisoutbursts can keep the stellar rotation rate close to some equilibrium valuefor which the angular momentum accretion rate is small. We show that thisequilibrium rotation rate may be similar to the observed rotation rates of TTauri stars; thus we propose that FU Orionis outbursts may be responsible forthe observed slow rotation of T Tauri stars. This mechanism is independent ofwhether the disk is disrupted by the stellar magnetic field during the T Tauriphase.Comment: 25 pages, LaTeX, uses aaspp4.sty, with 7 Postscript figures, tarred,  gzipped, uuencoded. To appear in the Astrophysical Journa

Can FU Orionis Outbursts Regulate the Rotation Rates of T Tauri Stars?