Search

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 ${\mu{\rm m}}$ to 36 mas at 13 ${\mu{\rm m}}$. 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 $\mu{\rm m}$) 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 ($4{-}250\times10^{-4}~\ensuremath{M_\odot}/\ensuremath{{\rm yr}}$) and that of a protoplanetary nebula with an equatorial mass excretion rate $\ga$$4 \times 10^{-5}\,\ensuremath{M_\odot}/\ensuremath{{\rm yr}}$. In both cases, taking the additional presence of an envelope or wind into account would result in lower mass flows.

We present N-band spectro-interferometric observations of the red supergiant WOH G64 in the Large Magellanic Cloud (LMC) using MIDI at the Very Large Telescope Interferometer (VLTI). The location of WOH G64 on the H-R diagram based on the previously estimated luminosities is in serious disagreement with the current stellar evolution theory. The dust envelope around WOH G64 has been spatially resolved with a baseline of ~60 m--the first MIDI observations to resolve an individual stellar source in an extragalactic system. The observed N-band visibilities show a slight decrease from 8 to 10 micron and a gradual increase longward of 10 micron, reflecting the 10 micron silicate feature in self-absorption. The visibilities measured at four position angles differing by ~60 degrees but at approximately the same baseline length (~60 m) do not show a noticeable difference, suggesting that the object appears nearly centrosymmetric. The observed N-band visibilities and spectral energy distribution can be reproduced by an optically and geometrically thick silicate torus model viewed close to pole-on. The luminosity of the central star is derived to be 2.8 x 10^5 Lsun, which is by a factor of 2 lower than the previous estimates based on spherical models. The lower luminosity newly derived from our MIDI observations and two-dimensional modeling brings the location of WOH G64 on the H-R diagram in much better agreement with theoretical evolutionary tracks for a 25 Msun star. We also identify the H2O absorption features at 2.7 and 6 micron in the spectra obtained with the Infrared Space Observatory and the Spitzer Space Telescope. The 2.7 micron feature originates in the photosphere and/or the extended molecular layers, while the 6 micron feature is likely to be of circumstellar origin., 9 pages, 6 figures, accepted for publication in A&A

8 pages; International audience; AMBER is the first near infrared focal instrument of the VLTI. It combines three telescopes and produces spectrally resolved interferometric measures. This paper discusses some preliminary results of the first scientific observations of AMBER with three Unit Telescopes at medium (1500) and high (12000) spectral resolution. We derive a first set of constraints on the structure of the circumstellar material around the Wolf Rayet gamma2 Velorum and the LBV eta Carinae.

AMBER is the first near infrared focal instrument of the VLTI. It combines three telescopes and produces spectrally resolved interferometric measures. This paper discusses some preliminary results of the first scientific observations of AMBER with three Unit Telescopes at medium (1500) and high (12000) spectral resolution. We derive a first set of constraints on the structure of the circumstellar material around the Wolf Rayet Gamma2 Velorum and the LBV Eta Carinae.