We have presented optical and X-ray photometry of V592 Her in quiescence obtained one year before the 1998 outburst. The R-band brightness of , flickering amplitude of mag, the large outburst amplitude of 10 mag, and the blue || color of are consistent with a nearly bare white dwarf with a low temperature of K and a distance of pc. Combining the empirical - relation for dwarf novae with the observed , and the correlation between and the outburst recurrence time with the observed , we have shown that the distance is likely to be significantly less than 1 kpc.
Given an orbital period of 1.5 hr, the presence of a main sequence secondary is unlikely, because the implied distance of pc is very difficult to reconcile with the observed outburst and quiescent magnitudes. This suggests that V592 Her contains a degenerate brown dwarf secondary and has passed through the period minimum of CVs, as has been speculated lately to be the case for TOADs in general (e.g. Politano et al. 1998). The low mass-transfer rate expected for a brown dwarf secondary is consistent with the non-detection in X-rays, the low bright-spot luminosity inferred from the small-amplitude flickering, the long inter-outburst timescale, and the low white dwarf temperature.
© European Southern Observatory (ESO) 1999
Online publication: February 23, 1999