OAO/MITSuME Photometry of Dwarf Novae. III. CSS130418:174033+414756

TL;DR

This study presents multicolour photometry of the dwarf nova CSS130418 during a superoutburst, revealing an extremely short superhump period, colour variations linked to brightness minima, and a revised mass ratio estimate.

Contribution

It provides new observational data on a dwarf nova with an exceptionally short superhump period and refines the system's mass ratio using superhump period analysis.

Findings

Superhump period of 0.046346 days, one of the shortest below the period minimum.

Bluest colour peaks coincide with brightness minima in superhumps.

Estimated mass ratio q = 0.077, larger than previous estimates.

Abstract

We report on multicolour photometry of the short period dwarf nova CSS130418:174033+414756 during the 2013 superoutburst. The system showed an unusually short superhump period with 0.046346(67) d during stage A, which is one of the shortest periods among dwarf novae below the period minimum. We found that the bluest peaks in $g' - I_{\rm c}$ colour variations tend to coincide with the brightness minima of the superhump modulations. We also studied nightly-averaged superhump amplitudes in $g'$, $R_{\rm c}$, and $I_{\rm c}$ bands and found that they have less dependence on wavelength. These properties are likely to be in common with dwarf novae exhibiting superhumps. We successfully obtained $g' - R_{\rm c}$ and $R_{\rm c} - I_{\rm c}$ colours during the temporal dip. The colour indices were significantly bluer compared with other dips of WZ Sge-type dwarf novae. By using the period of the growing superhumps, we estimated the mass ratio to be $q$ = 0.077(5), which is much larger than the previous study.