The Vicinity of the Galactic Supergiant B[e] Star CPD-57\deg2874 from Near- and Mid-IR Long Baseline Spectro-Interferometry with the VLTI (AMBER and MIDI)

Abstract

We present the first spectro-interferometric observations of the circumstellar envelope (CSE) of a B[e] supergiant (CPD−57°2874), performed with the Very Large Telescope Interferometer (VLTI) 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). Our 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. We show that a spherical dust model reproduces the SED but it underestimates the MIDI visibilities, suggesting that a dense equatorial disk is required to account for the compact dust-emitting region observed. Moreover, the derived major-axis position angle in the mid-IR (≅ 144°) agrees well with previous polarimetric data, hinting that the hot-dust emission originates in a disk-like structure. Our results support the non-spherical CSE paradigm for B[e] supergiants.