2020MNRAS.492.1154B

We report the analysis of time-series of infrared JHKs photometry of the dwarf nova V2051 Oph in quiescence with eclipse mapping techniques to investigate structures and the spectrum of its accretion disc. The light curves after removal of the ellipsoidal variations caused by the mass-donor star show a double-wave modulation signalling the presence of two asymmetric light sources in the accretion disc. Eclipse maps reveal two spiral arms on top of the disc emission, one at R_1= 0.28± 0.02 R_L1 and the other at R_2= 0.42± 0.02 R_L1 (where RL1 is the distance from disc centre to the inner Lagrangian point), which are seen face-on at binary phases consistent with the maxima of the double-wave modulation. The wide open angle inferred for the spiral arms (θs = 21° ± 4°) suggests the quiescent accretion disc of V2051 Oph has high viscosity. The accretion disc is hot and optically thin in its inner regions (T_gas∼ 10-12 x 10^3 K and surface densities ∼ 10^{-3} to 10^{-2} g cm^{-2}), and becomes cool and opaque in its outer regions.