The multiplicity of exoplanet host stars^*

New low-mass stellar companions of the exoplanet host stars HD 125612 and HD 212301

Astrophysikalisches Institut und Universitäts-Sternwarte Jena, Schillergäßchen 2-3, 07745 Jena, Germany e-mail: markus@astro.uni-jena.de

Received: 18 July 2008
Accepted: 31 October 2008

Abstract

Aims. We present new results from our ongoing multiplicity study of exoplanet host stars, carried out with SofI/NTT. We provide the most recent list of confirmed binary and triple star systems that harbor exoplanets.

Methods. We use direct imaging to identify wide stellar and substellar companions as co-moving objects to the observed exoplanet host stars, whose masses and spectral types are determined with follow-up photometry and spectroscopy.

Results. We found two new co-moving companions of the exoplanet host stars HD 125612 and HD 212301. HD 125612 B is a wide M 4 dwarf (0.18 ) companion of the exoplanet host star HD 125612, located about 1.5 arcmin (~4750 AU of projected separation) south-east of its primary. In contrast, HD 212301 B is a close M 3 dwarf (0.35 ), which is found about 4.4 arcsec (~230 AU of projected separation) north-west of its primary.

Conclusions. The binaries HD 125612 AB and HD 212301 AB are new members in the continuously growing list of exoplanet host star systems of which 43 are presently known. Hence, the multiplicity rate of exoplanet host stars is about 17%.