  Results of an analysis of the BRITE-Constellation and SMEI photometry and
radial-velocity observations, archival and new, of two single-lined
spectroscopic binary systems $\nu$ Centauri and $\gamma$ Lupi are reported. In
the case of $\gamma$ Lup AB, a visual binary, an examination of the light-time
effect shows that component A is the spectroscopic binary. Both $\nu$ Cen and
$\gamma$ Lup exhibit light variations with the orbital period. The variations
are caused by the reflection effect, i.e. heating of the secondary's hemisphere
by the early-B main sequence (MS) primary component's light. The modelling of
the light curves augmented with the fundamental parameters of the primary
components obtained from the literature photometric data and Hipparcos
parallaxes, shows that the secondary components are pre-MS stars, in the
process of contracting onto the MS. $\nu$ Cen and $\gamma$ Lup A are thus found
to be non-eclipsing counterparts of the B2 IV eclipsing binary (and a $\beta$
Cephei variable) 16 (EN) Lac, the B5 IV eclipsing binary (and an SPB variable)
$\mu$ Eri, and the recently discovered LMC nascent eclipsing binaries.
