OT J075418.7+381225 and OT J230425.8+062546: Promising Candidates for the Period Bouncer

TL;DR

This study analyzes two dwarf novae with unique superhump evolution, suggesting they are promising candidates for the elusive period bouncer stage, and estimates their population density to address the missing population issue.

Contribution

It identifies two dwarf novae as potential period bouncers based on their superhump properties and discusses their implications for the population of period bouncers.

Findings

Long superhump stage A indicates slow evolution due to small mass ratios.

Decline rates during superoutburst are lower than typical SU UMa-type DNe.

These objects may account for the missing population of period bouncers.

Abstract

We report on photometric observations of two dwarf novae, OT J075418.7+381225 and OT J230425.8+062546, which underwent superoutburst in 2013 (OT J075418) and in 2011 (OT J230425). Their mean period of the superhump was 0.0722403(26) d (OT J074518) and 0.067317(35) d (OT J230425). These objects showed a very long growing stage of the superhump (stage A) and a large period decrease in stage A-B transition. The long stage A suggests slow evolution of the superhump due to very small mass ratios of these objects. The decline rates during the plateau phase in the superoutburst of these objects were lower than those of SU UMa-type DNe with a similar superhump period. These properties were similar to those of SSS J122221.7-311523, the best candidate for the period bouncer. Therefore, these two DNe are regarded as good candidates for the period bouncer. We estimated the number density of period bouncers roughly from our observations in the recent five years. There is a possibility that these WZ Sge-type dwarf novae with unusual outburst properties can account for the missing population of the period bouncer expected from the evolutionary scenario.