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Accretion and ejection are tightly connected and represent the fundamentalmechanisms regulating star formation. However, the exact physical processesinvolved are not yet fully understood. We present high angular and spectralresolution observations of the Br Gamma emitting region in the Herbig Ae starHD163296 (MWC275) in order to probe the origin of this line and constrain thephysical processes taking place at sub-AU scales in the circumstellar region.By means of VLTI-AMBER observations at high spectral resolution (R~12000), westudied interferometric visibilities, wavelength-differential phases, andclosure phases across the Br Gamma line of HD163296. To constrain the physicalorigin of the Br Gamma line in Herbig Ae stars, all the interferometricobservables were compared with the predictions of a line radiative transferdisc wind model. The measured visibilities clearly increase within the Br Gammaline, indicating that the Br Gamma emitting region is more compact than thecontinuum. By fitting a geometric Gaussian model to the continuum-corrected BrGamma visibilities, we derived a compact radius of the Br Gamma emitting regionof ~0.07+/-0.02AU (Gaussian half width at half maximum; or a ring-fit radius of~0.08+/-0.02AU). To interpret the observations, we developed amagneto-centrifugally driven disc wind model. Our best disc wind model is ableto reproduce, within the errors, all the interferometric observables and itpredicts a launching region with an outer radius of ~0.04AU. However, theintensity distribution of the entire disc wind emitting region extends up to~0.16AU. Our observations, along with a detailed modelling of the Br Gammaemitting region, suggest that most of the Br Gamma emission in HD163296originates from a disc wind with a launching region that is over five timesmore compact than previous estimates of the continuum dust rim radius.

Probing the accretion-ejection connection with VLTI/AMBER: High spectral resolution observations of the Herbig Ae star HD163296