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We explore the multiplicity of exoplanet host stars with high-resolutionimages obtained with VLT/SPHERE. Two different samples of systems wereobserved: one containing low-eccentricity outer planets, and the othercontaining high-eccentricity outer planets. We find that 10 out of 34 stars inthe high-eccentricity systems are members of a binary, while the proportion is3 out of 27 for circular systems. Eccentric-exoplanet hosts are, therefore,significantly more likely to have a stellar companion than circular-exoplanethosts. The median magnitude contrast over the 68 data sets is 11.26 and 9.25,in H and K, respectively, at 0.30 arcsec. The derived detection limits revealthat binaries with separations of less than 50au are rarer for exoplanet hoststhan for field stars. Our results also imply that the majority ofhigh-eccentricity planets are not embedded in multiple stellar systems (24 outof 34), since our detection limits exclude the presence of a stellar companion.We detect the low-mass stellar companions of HD 7449 and HD 211847, bothmembers of our high-eccentricity sample. HD 7449B was already detected byRodigas et al (2016) and our independent observation is in agreement with thisearlier work. HD 211847's substellar companion, previously detected by theradial velocity method, is actually a low-mass star seen face-on. The role ofstellar multiplicity in shaping planetary systems is confirmed by this work,although it does not appear as the only source of dynamical excitation.

Eccentricity in planetary systems and the role of binarity: sample definition, initial results, and the system of HD 211847