SPHERE/ZIMPOL observations of the symbiotic system R: I. Imaging of the stellar binary and the innermost jet clouds

Context. R Aqr is a symbiotic binary system consisting of a mira variable, a hot companion with a spectacular jet outflow, and an extended emission line nebula. Because of its proximity to the Sun, this object has been studied in much detail with many types of high resolution imaging and interferometric techniques. We have used R Aqr as test target for the visual camera subsystem ZIMPOL, which is part of the new extreme adaptive optics (AO) instrument SPHERE at the Very Large Telescope (VLT). Aims. We describe SPHERE /ZIMPOL test observations of the R Aqr system taken in H alpha and other filters in order to demonstrate the exceptional performance of this high resolution instrument. We compare our observations with data from the Hubble Space Telescope (HST) and illustrate the complementarity of the two instruments. We use our data for a detailed characterization of the inner jet region of R Aqr. Methods. We analyze the high resolution approximate to 25 mas images from SPHERE /ZIMPOL and determine from the H alpha emission the position, size, geometric structure, and line fluxes of the jet source and the clouds in the innermost region