VLTI/AMBER and VLTI/MIDI spectro-interferometric observations of the B[e] supergiant CPD-57 2874

Abstract

We present the first high spatial and spectral observations of the circumstellar envelope (CSE) of a B[e] supergiant (CPD$-572874$), 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 $\simeq 1.8\times 3.4$ mas or $\simeq 4.5\times 8.5$ AU (adopting a distance of 2.5 kpc) at $2.2\micron$, and $\simeq 12\times 15$ mas or $\simeq 30\times 38$ AU at $12\micron$. The size of the region emitting the Br${\hat{I}}^3$ flux is $\simeq 2.8\times 5.2$ mas or $\simeq 7.0\times 13.0$ AU. The major-axis position angle of the elongated CSE in the mid-IR ($\simeq144\degr$) 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 ($UBV{R}_c{I}_c$) and near-IR ($JHKL$) broadband photometric observations of CPD$-572874$. Our spectro-interferometric VLTI observations and data analysis support the non-spherical CSE paradigm for B[e] supergiants.

Accepted by A&A