  As is the case for all techniques involved in the research for exoplanets,
direct imaging has to take into account the probability of so-called
astrophysical false positives, which are phenomena that mimic the signature of
objects we are seeking. In this work we aim to present a case of a false
positive found during a direct imaging survey conducted with VLT/NACO. A
promising exoplanet candidate was detected around the K2-type star HD\,8049 in
July 2010.Its contrast of $\Delta H$=7.05 at 1.57 arcsec allowed us to guess
the presence of a 35 \MJup companion at 50 projected AU, for the nominal system
age and heliocentric distance.To check whether it was gravitationally bound to
the host star, as opposed to an unrelated background object, we re-observed the
system one year later and concluded a high probability of a bound system. We
also used radial velocity measurements of the host star, spanning a time range
of $\sim$ 30 yr, to constrain the companion's mass and orbital properties, as
well as to probe the host star's spectral age indicators and general spectral
energy distribution. We also obtained for the companion $U$-band imaging with
EFOSC and $NIR$ spectroscopy. Combining all these information we conclude that
the companion of HD\,8049 is a white dwarf (WD), with temperature
$T_{eff}=18800 \pm 2100$ K and mass $M_{WD}=0.56 \pm 0.08 M_{\odot}$. The
significant radial velocity trend coupled with the imaging data indicate that
the most probable orbit has a semimajor axis of about 50 AU.The discrepancy
between the age indicators suggested against a bona-fide young star. The
moderately large level of chromospheric activity and fast rotation, mimicking
the properties of a young star, might be induced by the exchange of mass with
the progenitor of the WD. This example demonstrates some of the challenges in
determining accurate age estimates and identifications of faint companions.
