Resolving the B[e] star Hen 3-1191 at 10 $\mathsf{\mu}$m with VLTI/MIDI

Abstract

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.

Near infrared polarimetry of a sample of YSOs

“…This is consistent with scattering in an optically thin disk in Hen 3-1191. Lachaume et al (2007) resolved Hen 3-1191 at N band (8-13 μm) with VLTI/MIDI and found a disk PA of 1 • ±4 • .…”

“…5 high angular resolution (24-36 mas) of the data in Lachaume et al (2007), which maps the more interior disk region.…”

An interferometric journey around massive stars

“…These B[e] stars were perfect targets for the VLTI instruments MIDI and AMBER and the brightest of them were studied in the last decade : CPD -57 • 2874 (Domiciano de Souza et al 2007), Hen 3-1191 (Lachaume et al 2007), HD 87643 (Millour et al 2009a), HD 62623 (Meilland et al 2010), HD 50138 (Borges Fernandes et al 2011, MWC 300 (Wang et al 2012), HD 327083 (Wheelwright et al 2012), V921 Sco , and HD 85567 (Wheelwright et al 2013). Most of these study modeled either with simple geometric model or radiative transfer code such as MC3D, conclude that the dust was located in a circumstellar disk and that the gaseous emission was coming from structures smaller than the dusty-disk inner rim.…”

Fast ray-tracing algorithm for circumstellar structures (FRACS)

“…The next step after the toy models for the physical characterisation of the astrophysical objects can be made from the pure geometrical model towards the self-consistency by including and parameterising the object emissivity in the analysis. For instance, Lachaume et al (2007) and Malbet et al (2005) use optically thick (i.e. emitting as black bodies) and infinitely thin discs to model the circumstellar environment of pre-mainsequence and B[e] stars.…”