A resolved, au-scale gas disk around the B[e] star HD 50138 ^{⋆, ⋆⋆}

¹ Anton Pannekoek Institute, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
e-mail: lucas.ellerbroek@gmail.com
² Université Grenoble Alpes, IPAG, 38000 Grenoble, France
³ CNRS, IPAG, 38000 Grenoble, France
⁴ School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK
⁵ Observatório Nacional, Rua General José Cristino 77, 20921-400 São Cristovão, Rio de Janeiro, Brazil
⁶ Laboratoire Lagrange, UMR 7293 UNS-CNRS-OCA, Boulevard de l’Observatoire, CS 34229, 06304 Nice Cedex 4, France
⁷ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁸ Université de Lyon, 69003 Lyon, France
⁹ Université Lyon 1, Observatoire de Lyon, 9 avenue Charles André, 69230 Saint Genis Laval, France
¹⁰ CNRS, UMR 5574, Centre de Recherche Astrophysique de Lyon; École Normale Supérieure, 69007 Lyon, France
¹¹ The CHARA Array of Georgia State University, Mount Wilson Observatory, 91023 Mount Wilson CA, USA
¹² Department of Physics, University of Cincinnati, Cincinnati OH 45221, USA
¹³ Space Science Institute, 4750 Walnut Street, Boulder, CO 80303, USA
¹⁴ The Aerospace Corporation, Los Angeles, CA 90009, USA
¹⁵ Thule Scientific, Topanga, CA 90290, USA

Received: 6 May 2014
Accepted: 17 September 2014

Abstract

HD 50138 is a B[e] star surrounded by a large amount of circumstellar gas and dust. Its spectrum shows characteristics which may indicate either a pre- or a post-main-sequence system. Mapping the kinematics of the gas in the inner few au of the system contributes to a better understanding of its physical nature. We present the first high spatial and spectral resolution interferometric observations of the Brγ line of HD 50138, obtained with VLTI/AMBER. The line emission originates in a region more compact (up to 3 au) than the continuum-emitting region. Blue- and red-shifted emission originates from the two different hemispheres of an elongated structure perpendicular to the polarization angle. The velocity of the emitting medium decreases radially. An overall offset along the NW direction between the line- and continuum-emitting regions is observed. We compare the data with a geometric model of a thin Keplerian disk and a spherical halo on top of a Gaussian continuum. Most of the data are well reproduced by this model, except for the variability, the global offset and the visibility at the systemic velocity. The evolutionary state of the system is discussed; most diagnostics are ambiguous and may point either to a post-main-sequence or a pre-main-sequence nature.