Multi-wavelength photometry during the 2018 superoutburst of the WZ Sge-type dwarf nova EG Cancri

Abstract

We report on the multi-wavelength photometry of the 2018 superoutburst in EG Cnc. We have detected stage A superhumps and long-lasting late-stage superhumps via the optical photometry and have constrained the binary mass ratio and its possible range. The median value of the mass ratio is 0.048 and the upper limit is 0.057, which still implies that EG Cnc is one of the possible candidates for period bouncers. This object also showed multiple rebrightenings in this superoutburst which are the same as those in its previous superoutburst in 1996–1997, despite the difference in the main superoutburst. This would represent that the rebrightening type is inherent to each object and is independent of the initial disk mass at the beginning of superoutbursts. We also found that B − I and J − Ks colors were unusually red just before the rebrightening phase and became bluer during the quiescence between rebrightenings, which would mean that the low-temperature mass reservoir at the outermost disk accreted with time after the main superoutburst. Also, the ultraviolet flux was sensitive to rebrightenings as well as the optical flux, and the U − B color became redder during the rebrightening phase, which would indicate that the inner disk became cooler when this object repeated rebrightenings. Our results thus basically support the idea that the cool mass reservoir in the outermost disk is responsible for rebrightenings.

Investigation of WZ Sge-type Dwarf Nova ASASSN-19oc: Optical Spectroscopy and Multicolor Light Curve Analysis

“…Such systems are called "period bouncers" (Kolb & Baraffe 1999). Among the objects or candidates for these objects we can mention the studies of EG Cnc (Kimura et al 2021) Hence, the probability that there is a brown dwarf in our system is very high, and we draw the attention of researchers to this fact. For a more confident explanation of the physics of the processes occurring on the studied variable, it is necessary to obtain a radial velocity curve and calculate more accurate values of the masses of the components.…”

“…Based on the light curve shape, rebrightenings can be classified as long-duration, multiple, or single events (Imada et al 2006). For example, EZ Lyn showed 11 rebrightenings (Kato et al 2009b), ASASSN-15po had 10 rebrightenings (Kato 2015;Namekata et al 2017), EG Cnc exhibited 6 rebrightenings (Kimura et al 2021), and MASTER OT J211258.65+242145.4 displayed 8 rebrightenings (Nakata et al 2013), among others. The occurrence of rebrightenings can be associated with the behavior of the accretion disk.…”