The Galactic unclassified B[e] star HD 50138. II. Interferometric constraints on the close circumstellar environment

Context. HD 50138 is a southern star that presents the B[e] phenomenon, but its evolutionary stage is still not well known. This object presents spectral variability, which can be explained by outbursts or shell phases. Spectropolarimetric observations have shown the presence of a non-spherically symmetric circumstellar environment that is responsible for the B[e] phenomenon. However, up to now, the structure of the circumstellar medium of this object has not been studied deeply. <BR /> Aims: Based on recent optical long baseline interferometric observations from the VLTI/MIDI and VLTI/AMBER, and also from the Keck segment-tilting experiment, we study the structure of the circumstellar environment of HD 50138. <BR /> Methods: The analysis of our data is based on geometrical analytical modeling, also using the recent LITpro software and considering a large space of parameters, which allows us to obtain a good estimate of the geometry of the circumstellar medium of HD 50138, responsible for the emission in the H, K, and N-bands. <BR /> Results: We resolve the circumstellar environment of HD 50138 and describe its geometry for the first time in detail. Through analysis of multiwavelength data, the presence of a dusty circumstellar disk with an orientation onto the sky-plane of 71 ± 7°, which is perpendicular to the polarimetric measurements from the literature, was derived. We also derived that HD 50138 is seen under an intermediate angle related to the line of sight, 56 ± 4°. In addition, the structure of the disk and the flux contributions of the gas and dust components is discussed. <BR /> Conclusions: Based on analysis of different sets of interferometric data, we describe the circumstellar disk whose geometric parameters were determined, allowing us to understand the geometry of the circumstellar material of this bright star with the B[e] phenomenon. <P />Based on observations made with the ESO Very Large Telescope Interferometer at Paranal Observatory (Chile) under the Guarantied Time Observing, programs 080.C.0089, 080.D.0181 and 082.D.0047, and from the ESO archive.This research made use of the Jean-Marie Mariotti Center LITpro service co-developped by CRAL, LAOG and FIZEAU.