Imaging the spinning gas and dust in the disc around the supergiant A[e] star HD 62623^⋆

¹ Laboratoire FIZEAU, Université de Nice-Sophia Antipolis, Observatoire de la Côte d’Azur, 06108 Nice, France
e-mail: fmillour@oca.eu
² Max-Planck-Institute for Radioastronomy, Auf dem Hügel 69, 53121 Bonn, Germany
³ Departamento de Física y Astronomía, Universidad de Valparaíso, Errzuriz 1834, Valparaso, Chile
⁴ Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, Michigan 48109-1090, USA

Received: 24 November 2010
Accepted: 9 December 2010

Abstract

Context. To progress in the understanding of evolution of massive stars one needs to constrain the mass-loss and determine the phenomenon responsible for the ejection of matter an its reorganization in the circumstellar environment

Aims. In order to test various mass-ejection processes, we probed the geometry and kinematics of the dust and gas surrounding the A[e] supergiant HD 62623.

Methods. We used the combined high spectral and spatial resolution offered by the VLTI/AMBER instrument. Thanks to a new multi-wavelength optical/IR interferometry imaging technique, we reconstructed the first velocity-resolved images with a milliarcsecond resolution in the infrared domain.

Results. We managed to disentangle the dust and gas emission in the HD 62623 circumstellar disc. We measured the dusty disc inner rim, i.e. 6 mas, constrained the inclination angle and the position angle of the major-axis of the disc. We also measured the inner gaseous disc extension (2 mas) and probed its velocity field thanks to AMBER high spectral resolution. We find that the expansion velocity is negligible, and that Keplerian rotation is a favoured velocity field. Such a velocity field is unexpected if fast rotation of the central star alone is the main mechanism of matter ejection.

Conclusions. As the star itself seems to rotate below its breakup-up velocity, rotation cannot explain the formation of the dense equatorial disc. Moreover, as the expansion velocity is negligible, radiatively driven wind is also not a suitable explanation to explain the disc formation. Consequently, the most probable hypothesis is that the accumulation of matter in the equatorial plane is due to the presence of the spectroscopic low mass companion.