  The Optical Gravitational Lensing Experiment project has recently provided
the OGLE III list of low-luminosity object transits from campaigns #3 and #4,
reporting 40 new objects exhibiting the low-amplitude photometric eclipses
expected for exoplanets. Compared to previous OGLE targets, these OGLE III
candidates have been more restrictively selected and may contain low-mass
planets. We have secured follow-up low-resolution spectroscopy for 28
candidates out of this list (and one from the OGLE Carina fields) to obtain an
independent characterization of the primary stars by spectral classification
and thus better constrain the parameters of their companions. We fed the
constraints from these results back into an improved light curve solution.
Together with the radius ratios from the transit measurements, we derived the
radii of the low-luminosity companions. This allows us to examine the possible
sub-stellar nature of these objects. Sixteen of the companions can be clearly
identified as low-mass stars orbiting a main sequence primary, while 10 more
objects are likely to have red giant primaries and therefore also host a
stellar companion; 3 possibly have a sub-stellar nature R< 0.15 R_sun). The
planetary nature of these objects should therefore be confirmed by dynamical
mass determinations.
