AMBER/VLTI and MIDI/VLTI spectro-interferometric observations of the B[e] supergiant CPD-57°2874. Size and geometry of the circumstellar envelope in the near- and mid-IR

International audience; We present the first high spatial and spectral resolution observations of the circumstellar envelope (CSE) of a B[e] supergiant (CPD-57°2874), 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 ≃1.8×3.4 mas or ≃4.5×8.5 AU (adopting a distance of 2.5 kpc) at 2.2 μm, and ≃12×15 mas or ≃30×38 AU at 12 μm. The size of the region emitting the Brγ flux is ≃2.8×5.2 mas or ≃7.0×13.0 AU. The major-axis position angle of the elongated CSE in the mid-IR (≃144°) 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 (UBVR_cI_c) and near-IR (JHKL) broadband photometric observations of CPD-57°2874. Our spectro-interferometric VLTI observations and data analysis support the non-spherical CSE paradigm for B[e] supergiants. Based on observations collected at the European Southern Observatory, Paranal, Chile, within the AMBER science demonstration time programme 074.A-9026 and the MIDI open time programme 074.D-0101.