  We present the results of near-infrared, follow-up imaging and spectroscopic
observations at VLT, aimed at characterizing the long-period companions of the
exoplanet host stars HD196885, HD1237 and HD27442. The three companions were
previously discovered in the course of our CFHT and VLT coronographic imaging
survey dedicated to the search for faint companions of exoplanet host stars. We
used the NACO near-infrared adaptive optics instrument to obtain astrometric
follow-up observations of HD196885 A and B. The long-slit spectroscopic mode of
NACO and the integral field spectrograph SINFONI were used to carry out a
low-resolution spectral characterization of the three companions HD196885 B,
HD1237 B and HD27442 B between 1.4 and 2.5 microns. We can now confirm that the
companion HD196885 B is comoving with its primary exoplanet host star, as
previously shown for HD1237 B and HD27442 B. We find that both companions
HD196885 B and HD1237 B are low-mass stars of spectral type M1V and M4V
respectively. HD196885 AB is one of the closer (~23 AU) resolved binaries known
to host an exoplanet. This system is then ideal for carrying out a combined
radial velocity and astrometric investigation of the possible impact of the
binary companion on the planetary system formation and evolution. Finally, we
confirm via spectroscopy that HD27442 B is a white dwarf companion, the third
one to be discovered orbiting an exoplanet host star, following HD147513 and
Gliese 86. The detection of the broad Bracket gamma line of hydrogen indicates
a white dwarf atmosphere dominated by hydrogen.
