We present lightcurves of four binary subdwarf B stars , Ton 245 , Feige 11 , PG 1432+159 and PG 1017 - 086 .
We also present new spectroscopic data for PG 1017 - 086 from which we derive its orbital period , P = 0.073 d , and the mass function , f _ { m } = 0.0010 \pm 0.0002 \mbox { $ { M } _ { \odot } $ } .
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 PG 1432+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 PG 1017 - 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 .