The Galactic unclassified B[e] star HD 50138

II. Interferometric constraints on the close circumstellar environment^⋆,⋆⋆

¹ Observatório Nacional, Rua General José Cristino, 77, São Cristovão, 20921-400 Rio de Janeiro, Brazil
e-mail: borges@on.br
² Laboratoire H. Fizeau, UMR CNRS 6525, Université de Nice-Sophia Antipolis (UNS), Observatoire de la Côte d’Azur (OCA), Campus Valrose, 06108 Nice Cedex 2, France
e-mail: olivier.chesneau@obs-azur.fr; philippe.stee@obs-azur.fr, philippe.bendjoya@unice.fr; armando.domiciano@unice.fr; gilles.niccolini@unice.fr
³ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: meilland@mpifr-bonn.mpg.de, ; millour@mpifr-bonn.mpg.de,
⁴ Astronomický ústav, Akademie věd České republiky, Fričova 298, 251 65 Ondřejov, Czech Republic
e-mail: kraus@sunstel.asu.cas.cz

Received: 18 August 2010
Accepted: 13 December 2010

Abstract

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.

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.

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.

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.

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.