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HD50138 is a Herbig B[e] star with a circumstellar disc detected at IR and mmwavelength. Its brightness makes it a good candidate for NIR interferometryobservations. We aim to resolve, spatially and spectrally, the continuum andhydrogen emission lines in the 2.12-2.47 micron region, to shed light on theimmediate circumstellar environment of the star. VLTI/AMBER K-band observationsprovide spectra, visibilities, differential phases, and closure phases alongthree long baselines for the continuum, and HI emission in Br$\gamma$ and fivehigh-n Pfund lines. By computing the pure-line visibilities, we derive theangular size of the different line-emitting regions. A simple LTE model wascreated to constrain the physical conditions of HI emitting region. Thecontinuum region cannot be reproduced by a geometrical 2D elongated Gaussianfitting model. We estimate the size of the region to be 1 au. We find theBr$\gamma$ and Pfund lines come from a more compact region of size 0.4 au. TheBr$\gamma$ line exhibits an S-shaped differential phase, indicative ofrotation. The continuum and Br$\gamma$ line closure phase show offsets of$\sim$-25$\pm$5 $^o$ and 20$\pm$10$^o$, respectively. This is evidence of anasymmetry in their origin, but with opposing directions. We find that we cannotconverge on constraints for the HI physical parameters without a more detailedmodel. Our analysis reveals that HD50138 hosts a complex circumstellarenvironment. Its continuum emission cannot be reproduced by a simple discbrightness distribution. Similarly, several components must be evoked toreproduce the interferometric observables within the Br$\gamma$, line.Combining the spectroscopic and interferometric data of the Br$\gamma$ andPfund lines favours an origin in a wind region with a large opening angle.Finally, our results point to an evolved source.

The circumstellar environment of HD50138 revealed by VLTI/AMBER at high angular resolution