Follow-up spectroscopic observations of HD 107148 B: A new white dwarf companion of an exoplanet host star

We report on our follow-up spectroscopy of HD 1071478 B, a recently detected faint co-moving companion of the exoplanet host star HD 107148 A. The companion is separated from its primary star by about 35 '' (or 1790 AU of projected separation) and its optical and near infrared photometry is consistent with a white dwarf, located at the distance of HD 107148 A. In order to confirm the white dwarf nature of the co-moving companion, we obtained follow-up spectroscopic observations of HD 107148 B with CAFOS at the CAHA 2.2m telescope. According to our CAFOS spectroscopy HD 107148B is a DA white dwarf with an effective temperature in the range between 5900 and 6400 K. The properties of HD 107148 B can further be constrained with the derived effective temperature and the known visual and infrared photometry of the companion, using evolutionary models of DA white dwarfs. We obtain for HD 107148 B a mass of 0.56 +/- 0.05 M-circle dot, a luminosity of (2.0 +/- 0.2) x 10(-4) L-circle dot, log g [cm s(-2)]) = 7.95 +/- 0.09, and a cooling age of 2100 +/- 270 Myr. With its white dwarf companion the exoplanet host star HD 107148A forms an evolved stellar system, which hosts at least one exoplanet. So far, only few of these evolved systems are known, which represent only about 5% of all known exoplanet host multiple stellar systems. HD 107148 B is the second confirmed white dwarf companion of an exoplanet host star with a projected separation to its primary star of more than 1000 AU. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim