Gl86B: a white dwarf orbits an exoplanet host star

In this Letter we present our first high-contrast observations of the exoplanet host star Gl 86 using NAOS-CONICA (NACO) and its new Simultaneous Differential Imager (SDI) as well as results from NACO spectroscopy. Els et al. found a faint comoving companion located only similar to 2 arcsec east of the exoplanet host star Gl 86A. Our high-contrast SDI observations rule out additional stellar companions from 1 au up to 23 au, and are sensitive for faint T-dwarf companions down to 35 M-Jup. We present evidence for orbital motion of Gl 86B around the exoplanet host star Gl 86A, which finally confirms that this is a bound binary system. With the given photometry from Els et al. and the NACO spectroscopy obtained, we prove that the companion Gl 86B is a cool white dwarf with an effective temperature of 5000 +/- 500 K. This is the first confirmed white dwarf companion to an exoplanet host star and the first observational confirmation that planets survive the post-main-sequence evolution (giant phase and planetary nebula) of a star from which they are separated by only one to two dozen astronomical units, as expected from theory.