Superhumps and Repetitive Rebrightenings of the WZ Sge-Type Dwarf Nova, EG Cancri

• Published in: PASJ : publications of the Astronomical Society of Japan Vol. 56; no. 1; pp. S109 - S123
• Main Authors: Kato, Taichi, Nogami, Daisaku, Matsumoto, Katsura, Baba, Hajime
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford Universtiy Press 25.03.2004
• Subjects: accretion, accretion disks; stars : dwarf novae; stars : individual (EG Cancri); stars : novae, cataclysmic variables; stars: individual (EG Cancri); stars: dwarf novae; accretion, accretion disks; stars: novae, cataclysmic variables
• ISSN: 0004-6264; 2053-051X; 2053-051X
• DOI: 10.1093/pasj/56.sp1.S109

We report on time-resolved photometric observations of the WZ Sge-type dwarf nova, EG Cnc (Huruhata’s variable), during its superoutburst in 1996–1997. EG Cnc, after the main superoutburst accompanied by the development of superhumps typical of a WZ Sge-type dwarf nova, exhibited a series of six major rebrightenings. During these rebrightenings and the following long fading tail, EG Cnc persistently showed superhumps having a period equal to the superhump period observed during the main superoutburst. The persistent superhumps had a constant superhump flux with respect to the rebrightening phase. These findings suggest that the superhumps observed during the rebrightening stage and the fading tail are a “remnant” of the usual superhumps, and are not newly triggered by rebrightenings. By a comparison with the 1977 outburst of this object and outbursts of other WZ Sge-type dwarf novae, we propose an activity sequence of WZ Sge-type superoutbursts, in which the current outburst of EG Cnc is placed between a single-rebrightening event and distinct outbursts separated by a dip. The post-superoutburst behavior of WZ Sge-type dwarf novae can be understood in the presence of a considerable amount of remnant matter behind the cooling front in the outer accretion disk, even after the main superoutburst. We consider that a premature quenching of the hot state due to the weak tidal effect under the extreme mass ratio of the WZ Sge-type binary is responsible for the origin of the remnant mass.