Bozeman, MT, United States
Bozeman, MT, United States

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Namekata K.,Kyoto University | Isogai K.,Kyoto University | Kato T.,Kyoto University | Littlefield C.,University of Notre Dame | And 41 more authors.
Publications of the Astronomical Society of Japan | Year: 2017

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 an 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 82min, 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 a evolved secondary, (3) a binary with a metal-poor (Popullation II) seconday, or (4) a binary which was born with a brown-dwarf donor below the period minimum.


Kato T.,Kyoto University | Ishioka R.,National Taiwan University | Isogai K.,Kyoto University | Kimura M.,Kyoto University | And 66 more authors.
Publications of the Astronomical Society of Japan | Year: 2016

We observed RZ LMI, which is renowned for its extremely short (∼19 d) supercycle and is a member of a small, unusual class of cataclysmic variables called ERUMa-Type dwarf novae, in 2013 and 2016. In 2016, the supercycles of this object substantially lengthened in comparison to the previous measurements to 35, 32, and 60 d for three consecutive superoutbursts.We consider that the object virtually experienced a transition to the novalike state (permanent superhumper). This observed behavior reproduced the prediction of the thermal-Tidal instability model extremely well. We detected a precursor in the 2016 superoutburst and detected growing (stage A) superhumps with a mean period of 0.0602(1) d in 2016 and in 2013. Combined with the period of superhumps immediately after the superoutburst, the mass ratio is not as small as in WZ Sge-Type dwarf novae, having orbital periods similar to RZ LMI. By using least absolute shrinkage and selection operator (Lasso) two-dimensional power spectra, we detected possible negative superhumps with a period of 0.05710(1) d. We estimated an orbital period of 0.05792 d, which suggests a mass ratio of 0.105(5). This relatively large mass ratio is even above that of ordinary SUUMa-Type dwarf novae, and it is also possible that the exceptionally high mass-Transfer rate in RZ LMI may be a result of a stripped secondary with an evolved core in a system evolving toward an AM CVn-Type object. ©The Author 2016.

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