Superoutburst of ASASSN-15po

A paper entitled “Superoutburst of WZ Sge-type Dwarf Nova Below the Period Minimum: ASASSN-15po” has been accepted for publication in PASJ.
Preprint: ArXiv:1610.04941.

Namekata K., …, Neustroev V., et al.
We report on a superoutburst of a WZ Sge-type dwarf nova (DN), ASASSN-15po. The light curve showed the main superoutburst and multiple rebrightenings. In this outburst, we observed early superhumps and growing (stage A) superhumps with periods of 0.050454(2) and 0.051809(13) d, respectively. We estimated that the mass ratio of secondary to primary (q) is 0.0699(8) by using Porb and a superhump period Psh of stage A. ASASSN-15po [Porb∼ 72.6 min] is the first DN with the orbital period between 67-76 min. Although the theoretical predicted period minimum Pmin of hydrogen-rich cataclysmic variables (CVs) is about 65-70 min, the observational cut-off of the orbital period distribution at 80 min implies that the period minimum is about 82 min, and the value is widely accepted. We suggest the following four possibilities: the object is (1) a theoretical period minimum object (2) a binary with an evolved secondary (3) a binary with a metal-poor (Population II) secondary (4) a binary which was born with a brown-dwarf donor below the period minimum.

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