WZ Sge-type dwarf novae are characterized by long recurrence times of
outbursts (~10 yr) and short orbital periods (<~ 85 min). A significant part of
WZ Sge stars may remain undiscovered because of low outburst activity.
Recently, the observed orbital period distribution of cataclysmic variables
(CVs) has changed partly because outbursts of new WZ Sge stars have been
discovered routinely. Hence, the estimation of the intrinsic population of WZ
Sge stars is important for the study of the population and evolution of CVs. In
this paper, we present a Bayesian approach to estimate the intrinsic period
distribution of dwarf novae from observed samples. In this Bayesian model, we
assumed a simple relationship between the recurrence time and the orbital
period which is consistent with observations of WZ Sge stars and other dwarf
novae. As a result, the minimum orbital period was estimated to be ~70 min. The
population of WZ Sge stars exhibited a spike-like feature at the shortest
period regime in the orbital period distribution. These features are consistent
with the orbital period distribution previously predicted by population
synthesis studies. We propose that WZ Sge stars and CVs with a low
mass-transfer rate are excellent candidates for the missing population
predicted by the evolution theory of CVs.Comment: 9 pages, 5 figures, accepted for publication in PAS
