HOT INNER DISKS THAT APPEAR AND DISAPPEAR AROUND RAPIDLY ROTATING A-TYPE DWARFS

At any one time, approximately one-quarter of the most rapidly rotatin g normal A-type dwarfs (V sin i greater than or equal to 200 km s(-1)) show shell Lines of Ti II in the near-ultraviolet. Our observations d uring 22 years show that the lines appear and disappear on timescales of decades but do not display significant changes within 1 year. This implies that they are not remnants of the star formation but rather ar e probably caused by sporadic mass-loss events. A working hypothesis i s that all A-type stars that are rotating near their limits have these shells, but for only one-quarter of the time. Because these lines do not appear in stars with smaller sin i, the shells must be disks. Thes e are hot inner disks that may or may not be related to the cool outer disks seen by Smith and Terrile around beta Pic or through infrared e xcesses around Vega and other A-type dwarfs. The similar, limited line widths indicate that the disks are similar to 7 R above the stellar surfaces.