Infrared photometry of the dwarf nova V2051 Ophiuchi: II -- The quiescent accretion disc and its spiral arms

TL;DR

This study uses infrared eclipse mapping to reveal spiral arms in the quiescent accretion disc of dwarf nova V2051 Ophiuchi, indicating high viscosity and complex disc structure.

Contribution

First infrared eclipse mapping analysis of V2051 Ophiuchi's quiescent disc revealing spiral arms and their properties.

Findings

Detected two spiral arms at specific radii in the disc.

Disc exhibits high viscosity inferred from spiral arm opening angles.

Inner disc regions are hot and optically thin, outer regions are cooler and opaque.

Abstract

We report the analysis of time-series of infrared $JHK_s$ 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 $R_1= 0.28\pm 0.02 \,R_\mathrm{L1}$ and the other at $R_2= 0.42\pm 0.02 \,R_\mathrm{L1}$ (where $R_\mathrm{L1}$ 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 ($\theta_s= 21^o \pm 4^o$) suggests the quiescent accretion disc of V2051 Oph has high viscosity. The accretion disc is hot and optically thin in its inner regions ($T_\mathrm{gas}\sim 10-12 \times 10^3\,K$ and surface densities $\sim 10^{-3}-10^{-2}\,g\,cm^{-2}$), and becomes cool and opaque in its outer regions.