2015A&A...582A..44C

High angular and spectral resolution observations can provide us with fundamental clues to the complex circumstellar structure of young stellar objects (YSOs) and to the physical processes taking place close to these sources. We analyse the main physical parameters and the circumstellar environment of the young Herbig Be star HD 98922. We present AMBER/VLTI high spectral resolution (R =12000) interferometric observations across the Brγ line, accompanied by UVES high-resolution spectroscopy and SINFONI-AO assisted near-infrared (NIR) integral field spectroscopic data. To interpret our observations, we develop a magneto-centrifugally driven disc-wind model. Our analysis of the UVES spectrum shows that HD 98922 is a young (∼5x10⁵yr) Herbig Be star (SpT=B9V), located at a distance of 440±⁶⁰₅₀pc, with a mass accretion rate ({dot}(M)_acc) of ~(9±3 )x10^–7M_☉/yr. SINFONI K-band AO-assisted imaging shows a spatially resolved circumstellar disc-like region (∼140AU in diameter) with asymmetric brightness distribution. Our AMBER/VLTI UT observations indicate that the Brγ emitting region (ring-fit radius ∼0.31±0.04AU) is smaller than the continuum emitting region (inner dust radius ∼0.7±0.2AU), showing significant non-zero V-shaped differential phases (i.e. non S-shaped, as expected for a rotating disc). The value of the continuum-corrected pure Brγ line visibility at the longest baseline (89m) is ∼0.8±0.1, i.e. the Brγ emitting region is partially resolved. Our modelling suggests that the observed Brγ line-emitting region mainly originates from a disc wind with a half opening angle of 30°, and with a mass-loss rate ({dot}(M)_w) of ∼2x10^–7M_☉/yr. The observed V-shaped differential phases are reliably reproduced by combining a simple asymmetric continuum disc model with our Brγ disc-wind model. In conclusion, the Brγ emission of HD98922 can be modelled with a disc wind that is able to approximately reproduce all interferometric observations if we assume that the intensity distribution of the dust continuum disc is asymmetric.