ASASSN-16dt and ASASSN-16hg: Promising candidate period bouncers. (23rd April 2018)

• Record Type: Journal Article
• Authors: Kimura, Mariko; Isogai, Keisuke; Kato, Taichi; Taguchi, Kenta; Wakamatsu, Yasuyuki; Hambsch, Franz-Josef; Monard, Berto; Myers, Gordon; Dvorak, Shawn; Starr, Peter; Brincat, Stephen M; de Miguel, Enrique; Ulowetz, Joseph; Itoh, Hiroshi; Stone, Geoff; Nogami, Daisaku
• Is Part Of: Publications of the Astronomical Society of Japan. Volume 70:Number 3(2018:Jun.)
• Publication Date: 2018-04-23
• Subjects: accretion, accretion disks -- novae, cataclysmic variables -- stars: dwarf novae -- stars: individual (ASASSN-16dt, ASASSN-16hg); Astronomy -- Periodicals; 520.5
• DOI: 10.1093/pasj/psy037
• Languages: English
• ISSNs: 0004-6264

Abstract

Abstract: We present optical photometry of superoutbursts that occurred in 2016 of two WZ Sge-type dwarf novae (DNe), ASASSN-16dt and ASASSN-16hg. Their light curves showed a dip in brightness between the first plateau stage with no ordinary superhumps (or early superhumps) and the second plateau stage with ordinary superhumps. We find that the dip is produced by the slow evolution of the 3 : 1 resonance tidal instability and that it would likely be observed in low mass-ratio objects. An estimated mass ratio ( q ≡ M 2 / M 1 ) from the period of developing (stage A) superhumps [0.06420(3) d] was 0.036(2) in ASASSN-16dt. Additionally, its superoutburst has many properties similar to those in other low- q WZ Sge-type DNe: long-lasting stage-A superhumps, small superhump amplitudes, long delay of ordinary-superhump appearances, and a slow decline rate in the plateau stage with superhumps. Its very small mass ratio and observational characteristics suggest that this system is one of the best candidates for a period bouncer—a binary accounting for the missing population of post-period minimum cataclysmic variables. Although it is not clearly verified due to the lack of detection of stage-A superhumps, ASASSN-16hg might be a possible candidate for period bouncers on the basis of the morphology of its light curves and the small superhump amplitudes. Many outburst properties of period bouncer candidates would originate from the small tidal effects of their secondary stars.