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

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We report the analysis of time-series of infrared JHKₛ photometry of the dwarf nova V2051 Oph in quiescence. We modelled the ellipsoidal variations caused by the distorted mass-donor star to infer its JHKₛ fluxes. From its infrared colors we estimate a spectral type of M(8.0± 1.5) and an equivalent blackbody temperature of TBB=(2700±270)K. We used the Barnes & Evans relation to infer a photometric parallax distance of dBE=(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.