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 resolution observations of the circumstellar envelope (CSE) of a B[e] supergiant (CPD-57 degrees 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 similar or equal to 1.8 x 3.4 mas or similar or equal to 4.5 x 8.5 AU (adopting a distance of 2.5 kpc) at 2.2 mu m, and similar or equal to 12 x 15 mas or similar or equal to 30 x 38 AU at 12 mu m. The size of the region emitting the Br gamma flux is similar or equal to 2.8 x 5.2 mas or similar or equal to 7.0 x 13.0 AU. The major- axis position angle of the elongated CSE in the mid-IR (similar or equal to 144 degrees) 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 (UBVRcIc) and near-IR (JHKL) broadband photometric observations of CPD-57 degrees 2874. Our spectro-interferometric VLTI observations and data analysis support the non- spherical CSE paradigm for B[e] supergiants.