A1 Refereed original research article in a scientific journal
Superoutburst of WZ Sge-type dwarf nova below the period minimum: ASASSN-15po
Authors: Kosuke Namekata, Keisuke Isogai, Taichi Kato, Colin Littlefield, Katsura Matsumoto, Naoto Kojiguchi, Yuki Sugiura, Yusuke Uto, Daiki Fukushima, Taiki Tatsumi, Eiji Yamada, Taku Kamibetsunawa, Enrique de Miguel, William L. Stein, Richard Sabo, Maksim V. Andreev, Etienne Morelle, E. P. Pavlenko, Julia V. Babina, Alex V. Baklanov, Kirill A. Antonyuk, Okasana I. Antonyuk, Aleksei A. Sosnovskij, Sergey Yu. Shugarov, Polina Yu. Golysheva, Natalia G. Gladilina, Ian Miller, Vitaly V. Neustroev, Vahram Chavushyan, José R. Valdés, George Sjoberg, Yutaka Maeda, Hiroshi Itoh, Gianluca Masi, Raúl Michel, Pavol A. Dubovsky, Seiichiro Kiyota, Tamás Tordai, Arto Oksanen, Javier Ruiz, Daisaku Nogami
Publisher: Oxford University Press
Publication year: 2017
Journal: Publications- Astronomical Society of Japan
Journal acronym: PASJ
Volume: 69
Issue: 1
Number of pages: 9
ISSN: 0004-6264
DOI: https://doi.org/10.1093/pasj/psw107
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 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 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.
