Gravitational lensing in eclipsing binary stars

I consider the effect of the gravitational deflection of Light upon the lig ht curves of eclipsing binary stars, focusing mainly upon systems containin g at least one white dwarf component. In absolute terms the effects are sma ll, however they are strongest at the time of secondary eclipse when the wh ite dwarf transits its companion, and act to reduce the depth of this featu re. If not accounted for, this may lead to under-estimation of the radius o f the white dwarf compared with that of its companion. I show that the effe ct is significant for plausible binary parameters, and that it leads to sim ilar to 25 per cent reduction in the transit depth in the system KPD 1930+2 752. The reduction of eclipse depth is degenerate with the stellar radius r atio, and therefore cannot be used to establish the existence of lensing. A second-order effect of the light bending is to steepen the ingress and egr ess features of the secondary eclipse relative to the primary eclipse, alth ough it will be difficult to see this in practice. I consider also binaries containing neutron stars and black holes. I conclude that, although relati vely large effects are possible in such systems, a combination of rarity, f aintness and intrinsic variability makes it unlikely that lensing will be d etectable in them.