AMBER/VLTI and MIDI/VLTI spectro-interferometric observations of the B[e] supergiant CPD^*

Size and geometry of the circumstellar envelope in the near- and mid-IR

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
² Laboratoire Universitaire d'Astrophysique de Nice, UMR 6525 Université de Nice – Sophia Antipolis/CNRS, Parc Valrose, 06108 Nice Cedex 2, France
³ Laboratoire Gemini, UMR 6203 Observatoire de la Côte d'Azur/CNRS, BP 4229, 06304 Nice Cedex 4, France
⁴ Dept. of Physics and Astronomy, PO Box 26170, University of North Carolina at Greensboro, Greensboro, NC 27402 6170, USA
⁵ INAF-Osservatorio Astrofisico di Arcetri, Istituto Nazionale di Astrofisica, Largo E. Fermi 5, 50125 Firenze, Italy
⁶ Laboratoire d'Astrophysique de Grenoble, UMR 5571 Université Joseph Fourier/CNRS, BP 53, 38041 Grenoble Cedex 9, France
⁷ European Southern Observatory, Karl Schwarzschild Strasse 2, 85748 Garching, Germany

Received: 31 August 2005
Accepted: 17 October 2005

Abstract

We present the first high spatial and spectral resolution observations of the circumstellar envelope (CSE) of a B[e] supergiant (CPD), performed with the Very Large Telescope Interferometer (VLTI). Spectra, visibilities and closure phase were obtained using the beam-combiner instruments AMBER (near-IR interferometry with three 8.3 m Unit Telescopes or UTs) and MIDI (mid-IR interferometry with two UTs). The interferometric observations of the CSE are well fitted by an elliptical Gaussian model with FWHM diameters varying linearly with wavelength. Typical diameters measured are mas or AU (adopting a distance of 2.5 kpc) at , and mas or AU at . The size of the region emitting the Brγ flux is mas or AU. The major-axis position angle of the elongated CSE in the mid-IR () agrees well with previous polarimetric data, hinting that the hot-dust emission originates in a disk-like structure. In addition to the interferometric observations we also present new optical () and near-IR () broadband photometric observations of CPD. Our spectro-interferometric VLTI observations and data analysis support the non-spherical CSE paradigm for B[e] supergiants.