Abstract
Abstract We observed the 1994, 1996, and 2001 outbursts of HO Del. From the detection of secure superhumps, HO Del is confirmed to be an SU UMa-type dwarf nova with a superhump period of 0.06453(6)d. Based on recent observations and past records, the outbursts of HO Del are found to be relatively rare, with the shortest intervals of superoutbursts being $\sim 740 \,\mathrm{d}$. Among SU UMa-type dwarf novae with similar outburst intervals, the outburst amplitude ($\sim 5.0 \,\mathrm{mag}$) is unusually small. HO Del showed a rather rapid decay of the superhump amplitudes, and no regrowth of the amplitudes during the later stage, in contrast to the commonly observed behavior in SU UMa-type dwarf novae with long outburst intervals. We positively identified HO Del with a ROSAT X-ray source, and obtained a relatively large X-ray luminosity of $10^{31.1 \pm 0.2} \,\mathrm{erg} \,\mathrm{s}^{-1}$. We also performed a literature survey of SU UMa-type dwarf novae and presented a new set of basic statistics. The SU UMa-type dwarf novae with a brightening trend or with a regrowth of superhumps near the termination of a superoutburst are found to be rather tightly confined in a small region on the (superhump period–supercycle length) plane. These features may provide a better observational distinction for the previously claimed subgroup of dwarf novae (Tremendous Outburst Amplitude Dwarf Novae).
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