A Lucky Imaging search for stellar sources near 74 transit hosts

Context. Many transiting-planet host stars lack high-resolution imaging so that close stellar sources can be missed. Those unknown stars potentially bias the derivation of the planetary and stellar parameters from the transit light curve, regardless of whether they are bound or not. In addition, bound stellar companions interact gravitationally with the exoplanet host star, the disk, and the planets and can thus influence the formation and evolution of the planetary system strongly. Aims. We extended our high-resolution Lucky Imaging survey for close stellar sources by 74 transiting-planet host stars. Thirty-nine of these stars lack previous high-resolution imaging, 23 are follow up observations of companions or companion candidates, and the remaining stars have been observed by others with AO imaging but in different bands. We determine the separation of all new and known companion candidates and estimate the flux ratio in the observed bands. Methods. All observations were carried out with the Lucky Imaging camera AstraLux Norte at the Calar Alto 2 : 2 m telescope in i' and z' passbands. Results. We find new stellar sources within 1 '' of HAT-P-27, HAT-P-28, HAT-P-35, WASP-76, and WASP-103 and between 1 '' and 4 '' of HAT-P-29 and WASP-56.