Gl86B: a white dwarf orbits an exoplanet host star

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In this letter we present our first high contrast NACO/SDI observations of the exoplanet host star Gl86 and results from NACO spectroscopy. Els et al. (2001) found a faint co-moving companion located only 2arcsec east of the exoplanet host star Gl86A. Our high contrast SDI observations rule out additional stellar companions from 1AU up to 23AU, and are sensitive for faint T dwarf companions down to 35MJup. We present evidence for orbital motion of Gl86B around the exoplanet host star Gl86A, which finally confirms that this is a bound binary system. With the given photometry from Els et al. (2001) and the obtained NACO spectroscopy we prove that the companion Gl86B is a cool white dwarf with an effective temperature of 5000+-500K. 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 of a star from which they are separated by only one to two dozen astronomical units (giant phase and planetary nebula) as expected from theory.