ASASSN-16dt and ASASSN-16hg: Promising candidate period bouncers

作者：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

来源：Publications of the Astronomical Society of Japan, 2018, 70(3): 47.

DOI：10.1093/pasj/psy037

• accretion, accretion disks
• novae, cataclysmic variables
• stars: dwarf novae
• stars: individual (ASASSN-16dt, ASASSN-16hg)

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.

• 出版日期2018-6