Infrared photometry of WY Sge: just an ordinary old nova?

Abstract

We present IR photometry of the eclipsing old nova WY Sge (Nova Sagittae 1783), for which we derive a new ephemeris. The ratio of light from the disc and white dwarf to that of the secondary star is typical for an old nova, but at least nine times larger than that of similar period eclipsing dwarf novae. To account for the phase of maximum light it is necessary to invoke some heating of the inner face of the Roche lobe filling star. From this we infer that the heating energy absorbed is 25 ± 10 per cent of the intrinsic luminosity of the secondary. The colours in and out of the eclipse are used to set limits on the distance and reddening. The dereddened colours are compared with other old novae; there appears to be no significant difference. We conclude that WY Sge is not a dwarf nova and thus has remained at a high mass transfer rate. We suggest that if the mass transfer is driven by irradiation then it is unlikely to decrease in the near future. In any case, models suggest that the irradiation measured is unlikely to be sufficient to drive the observed mass transfer rate.