[O I] sub-arcsecond study of a microjet from an intermediate mass young star: RY Tauri

Context. High-resolution studies of microjets in T Tauri stars (cTTs) reveal key information on the jet collimation and launching mechanism, but only a handful of systems have been mapped so far. Aims. We wish to perform a detailed study of the microjet from the 2 M circle dot young star RY Tau, to investigate the influence of its higher stellar mass and claimed close binarity on jet properties. Methods. Spectro-imaging observations of RY Tau were obtained in [O I]lambda 6300 with resolutions of 0''.4 and 135 km s(-1), using the integral field spectrograph OASIS at the Canada-France-Hawaii Telescope. Deconvolved images reach a resolution of 0''.2. Results. The blueshifted jet is detected within 2'' of the central star. We determine its PA, collimation, 2D kinematics, mass-flux rate, ejection to accretion ratio, and transverse velocity shifts taking accurately into account errors due to finite signal to noise ratio. The RY Tau system is shown to provide important constraints to several models of steady MHD ejection. Conclusions. The remarkably similar properties of the RY Tau microjet compared to jets from lower mass cTTs gives support to the common belief that the jet launching mechanism is universal over a broad range of stellar masses. The proximity between the jet PA and the PA of the photocenter variations observed by Hipparcos calls into question the interpretation of the latter in terms of binarity of RY Tau. Partial occultation events of the photosphere may offer an alternative explanation.