Gl86B: a white dwarf orbits an exoplanet host star

Abstract

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.