An extreme-AO search for giant planets around a white dwarf^⋆,⋆⋆

VLT/SPHERE performance on a faint target GD 50

¹ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
e-mail: sxu@eso.org
² European Southern Observatory, Alonso de Cordova 3107, Vitacura, 19001 Casilla, Santiago 19, Chile
³ Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
⁴ Kiel University, Institute of Theoretical Physics and Astrophysics, Leibnizstr. 15, 24118 Kiel, Germany

Received: 24 March 2015
Accepted: 15 June 2015

Abstract

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.