Infrared photometry of the dwarf nova V2051 Ophiuchi – I. The mass-donor star and the distance★

Abstract

We report the analysis of time-series of infrared JHK s photometry of the dwarf nova V2051 Oph in quiescence. We modelled the ellipsoidal variations caused by the distorted mass-donor star to infer its JHK s fluxes. From its infrared colors we estimate a spectral type of M(8.0 ± 1.5) and an equivalent blackbody temperature of T BB = (2700 ± 270) K. We used the Barnes & Evans relation to infer a photometric parallax distance of d BE = (102 ± 16) pc to the binary. At this short distance, the corresponding accretion disc temperatures in outburst are too low to be explained by the disc-instability model for dwarf nova outbursts, underscoring a previous suggestion that the outbursts of this binary are powered by mass-transfer bursts.