Resolving the B[e] star Hen 3-1191 at 10 μm with VLTI/MIDI

We report spatially resolved, spectrally dispersed N-band observations of the B[e] star Hen 3-1191 with the MIDI instrument of the Very Large Telescope Interferometer. The object is resolved with a 40 m baseline and has an equivalent uniform disc diameter ranging from 24 mas at 8 μm} to 36 mas at 13 {μm}. The MIDI spectrum and visibilities show a curvature which can arise from a weak silicate feature in which the object appears ≈15% larger than in the continuum, but this could result from a change in the object's geometry within the band. We then model Hen's 3-1191 spectral energy distribution (.4-60 μm) and N-band visibilities. Because of the unknown nature of the object, we use a wide variety of models for objects with IR excesses. We find the observations to be consistent with a disc featuring an unusually high mass accretion and a large central gap almost void of matter, an excretion disc, and a binary made of two IR sources. We are unable to find a circumstellar shell model consistent with the data. We review the different hypotheses concerning the physical nature of the star and conclude that it is neither a Be supergiant nor a symbiotic star. However, we could not discriminate between the scenario of a young stellar object featuring an unusually strong FU Orionis-like outburst of mass accretion (4-250×10^-4 M_⊙/{yr}) and that of a protoplanetary nebula with an equatorial mass excretion rate ⪆4 × 10^-5 M_⊙/yr. In both cases, taking the additional presence of an envelope or wind into account would result in lower mass flows.

Based on observations made with the Very Large Telescope Interferometer of the European Southern Observatory. Programme ID: 073.C-0757.