Context : 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 .

Aims : 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 M _ { \mathrm { Jup } } companion at 50 projected AU , for the nominal system age and heliocentric distance .

Methods : 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 .

Results : Combining all these information we conclude that the companion of HD 8049 is a white dwarf ( WD ) , with temperature T _ { \mathrm { eff } } = 18800 \pm 2100 K and mass M _ { \mathrm { 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 .

Conclusions :