Transient infall events in the disk of AB Aurigae: The beta Pictoris phenomenon at 2-4 megayears

Surveys of Herbig Ae/Be stars have indicated that infalling, circumstellar gas similar to that routinely detected toward beta Pic is preferentially ob served close to the disk midplane. Recent millimeter interferometry of the historically prototypical Herbig Ae star, AB Aur, indicates that this star is viewed slightly above the disk midplane (i = 76 degrees). The wealth of archival spectroscopic data for this star makes it an ideal test of the geo metry for infalling or accreting gas in these stars. We present a review of the extant IUE and Hubble Space Telescope GHRS spectral data for AB Aur an d find, in contrast to previous studies of this star, which focused on Mg I I, that infalling gas is detected at all epochs with covering factors simil ar to those reported for HD 100546 and that an episode of enhanced infall w as serendipitously detected during the 1990 monitoring run.