UNUSUAL STUNTED OUTBURSTS IN OLD NOVAE AND NOVA-LIKE CATACLYSMIC VARIABLES

Outbursts averaging 0.6 mag in amplitude and 10 days in width are desc ribed in five old novae and nova-like cataclysmic variables: UU Aqr, Q Cyg, CP Lac, X Ser, and RW Sex. These stars are thought to be high ma ss transfer rate systems for which the accretion disk is expected to b e stable against the thermal instability responsible for dwarf nova ou tbursts. The widths and spacings of these events are similar to those of dwarf nova eruptions, but the amplitudes are significantly smaller, or ''stunted. '' The outbursts are sometimes accompanied by dips. The se dips have amplitudes that are similar to the outbursts' but have sh apes that scatter significantly more than the shapes of the outbursts. The outbursts and dips sometimes occur as pairs and are sometimes iso lated. We are not able at this time to determine a single common mecha nism for this behavior, or even to conclude that some mechanisms are p referred. Rather, we characterize these phenomena with regard to outbu rst shapes and frequency of occurrence and explore a range of possible causes, including truncated disks, mass transfer modulations, and Z C amelopardalis type behavior. Arguments are assembled for and against s uch possible mechanisms, and key observations are suggested. It appear s unlikely that accretion disk instabilities are the single common cau se of these phenomena, and we are left with either a combination of ac cretion disk and mass transfer events or a situation in which mass tra nsfer events are somehow responsible for all these varied behaviors.