An extreme-AO search for giant planets around a white dwarf - VLT/SPHERE performance on a faint target GD 50

Context. Little is known about the planetary systems around single white dwarfs, although there is strong evidence that they do exist. Aims. We performed a pilot study with the extreme-AO system on the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) on the Very Large Telescopes (VLT) to look for giant planets around a young white dwarf, GD 50. Methods. We were awarded science verification time on the new ESO instrument SPHERE. Observations were made with the InfraRed Dual-band Imager and Spectrograph in classical imaging mode in H band. Results. Despite the faintness of the target (14.2 mag in R band), the AO loop was closed and a strehl of 37% was reached in H band. No objects were detected around GD 50. We achieved a 5-sigma contrast of 6.2, 8.0, and 8.25 mag at 0”.2, 0”.4, and 0”.6 and beyond, respectively. We exclude any substellar objects more massive than 4.0 M-J at 6.2 au, 2.9 M-J at 12.4 au, and 2.8 M-J at 18.6 au and beyond. This rivals the previous upper limit set by Spitzer. We further show that SPHERE is the most promising instrument available to search for close-in substellar objects around nearby white dwarfs.