Sub-0.1" optical imaging of the Z CMa jets with SPHERE/ZIMPOL

Context. Crucial information on the mass accretion-ejection connection in young stars can be obtained from high spatial resolution images of jets in sources with known recurrent accretion outbursts. Aims. Using the VLT /SPHERE ZIMPOL instrument, we observed the young binary Z CMa that is composed of a Herbig Be star and a FUor object, both driving a jet. We aim to analyse the structure of the two jets, their relation with the properties of the driving sources, and their connection with previous accretion events observed in this target. Methods. We obtained optical images in the H alpha and[Oi] 6300 angstrom lines at the unprecedented angular resolution 0.03 arc sec, on which we have performed both continuum subtraction and deconvolution, thereby deriving results that are consistent with each other. Results. Our images reveal extended emission from both sources: a fairly compact and poorly collimated emission SW of the Herbig component and an extended collimated and precessing jet from the FUor component. The compact emission from the Herbig star is compatible with a wideangle wind and is possibly connected to the recent outburst events shown by this component. The FUor jet is traced down to 70 mas ( 80 AU) from the source and is highly collimated with a width of 26-48 AU at distances 100-200 AU, which is similar to the width of jets from T Tauri stars. This strongly suggests that the same magneto-centrifugal jet-launching mechanism also operates in FUors. The observed jet wiggle can be modelled as originating from an orbital motion with a period of 4.2 yr around an unseen companion with mass between 0.48 and 1 M-circle dot. The jet mass loss rate. M jet was derived from the [Oi] luminosity and comprises of between 1 x 10(8) and 1 x 10(6) M-circle dot yr(-1). This is the first direct. M-jet measurement from a jet in a FUor. If we assume previous mass accretion rate estimates obtained through modelling of the accretion disk, the derived range of. M jet would imply a very low mass-ejection e ffi ciency (M-jet/M-acc less than or similar to 0.02), which is lower than that typical of T Tauri stars.