  We present lightcurves of four binary subdwarf B stars, Ton 245, Feige 11,
PG1432+159 and PG1017-086. We also present new spectroscopic data for
PG1017-086 from which we derive its orbital period, P=0.073d, and the mass
function, f_m = 0.0010 +/- 0.0002 solar masses. This is the shortest period for
an sdB binary measured to-date. The values of P and f_m for the other sdB
binaries have been published elsewhere. We are able to exclude the possibility
that the unseen companion stars to Ton 245, Feige 11 and PG1432+159 are
main-sequence stars or sub-giant stars from the absence of a sinusoidal signal
which would be caused by the irradiation of such a companion star, i.e., they
show no reflection effect. The unseen companion stars in these binaries are
likely to be white dwarf stars. By contrast, the reflection effect in
PG1017-086 is clearly seen. The lack of eclipses in this binary combined with
other data suggests that the companion is a low mass M-dwarf or, perhaps, a
brown dwarf.
