Superhumps in a Rarely Outbursting SU UMa-Type Dwarf Nova, HO Delphini

We observed the 1994, 1996 and 2001 outbursts of HO Del. From the detectionof secure superhumps, HO Del is confirmed to be an SU UMa-type dwarf nova witha superhump period of 0.06453(6) d. Based on the recent observations and thepast records, the outbursts of HO Del are found to be relatively rare, with theshortest intervals of superoutbursts being ~740 d. Among SU UMa-type dwarfnovae with similar outburst intervals, the outburst amplitude (~5.0 mag) isunusually small. HO Del showed a rather rapid decay of the superhumpamplitudes, and no regrowth of the amplitudes during the later stage, incontrast to the commonly observed behavior in SU UMa-type dwarf novae with longoutburst intervals. We positively identified HO Del with a ROSAT X-ray source,and obtained a relatively large X-ray luminosity of 10^(31.1+/-0.2) erg/s. Wealso performed a literature survey of SU UMa-type dwarf novae, and presented anew set of basic statistics. The SU UMa-type dwarf novae with a brighteningtrend or with a regrowth of superhumps near the termination of a superoutburstare found to be rather tightly confined in a small region on the (superhumpperiod-supercycle length) plane. These features may provide a betterobservational distinction for the previously claimed subgroup of dwarf novae(Tremendous Outburst Amplitude Dwarf Novae).Comment: 17 pages, 12 figures, accepted for publication in PAS