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

We present the first high spatial and spectral observations of the circumstellar envelope (CSE) of a B[e] supergiant (CPD-5't' 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 FVVHM diameters varying linearly with wavelength. Typical diameters measured are ~ 1.8 X 3.4 mas or ~ 4.5 X 8.5 AU (adopting a distance of 2.5 kpc) at 2.2 pm, and ~ 12 X 15 mas or ~ 30 X 38 AU at 12 pm. The size of the region emitting the Brr flux is ~ 2.8 X 5.2 mas or ~ 7.0 X 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 (UBVRclc) 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.