Magnetospheres and Disk Accretion in Herbig Ae/Be Stars

We present evidence of magnetically-mediated disk accretion in Herbig Ae/Bestars. Magnetospheric accretion models of Balmer and sodium profiles calculatedwith appropriate stellar and rotational parameters are in qualitative agreementwith the observed profiles of the Herbig Ae star UX Ori, and yield a massaccretion rate of ~ 10^{-8} Msun/yr. If more recent indications of an extremelylarge rotation rate for this object are correct, the magnetic field geometrymust deviate from that of a standard dipole in order to produce line emissionconsistent with observed flux levels. Models of the associated accretion shockqualitatively explain the observed distribution of excess fluxes in the Balmerdiscontinuity for a large ensemble of Herbig Ae/Be stars, and imply typicallysmall mass accretion rates, < 10^{-7} Msun/yr. In order for accretion toproceed onto the star, significant amounts of gas must exist inside the dustdestruction radius, which is potentially problematic for recently advocatedscenarios of "puffed" inner dust wall geometries. However, our models of theinner gas disk show that for the typical accretion rates we have derived, thegas should be generally optically thin, thus allowing direct stellarirradiation of the inner dust edge of the disk.Comment: 32 pages, 12 figures, accepted by Ap