The close circumstellar environment of the semi-regular S-type star Pi^1 Gruis

Abstract

We study the close circumstellar environment of the nearby S-type star Pi^1 Gruis using high spatial-resolution, mid-infrared observations from the ESO/VLTI. Spectra and visibilities were obtained with the MIDI interferometer on the VLT Auxiliary Telescopes. The cool M5III giant Beta Gruis was used as bright primary calibrator, and a dedicated spectro-interferometric study was undertaken to determine its angular diameter accurately. The MIDI measurements were fitted with the 1D numerical radiative transfer code DUSTY to determine the dust shell parameters of Pi^1 Gruis. Taking into account the low spatial extension of the model in the 8-9 $\mu$m spectral band for the smallest projected baselines, we consider the possibility of a supplementary molecular shell. The MIDI visibility and phase data are mostly dominated by the spherical 21 mas (694 Rsol) central star, while the extended dusty environment is over-resolved even with the shortest baselines. No obvious departure from spherical symmetry is found on the milliarcsecond scale. The spectro-interferometric observations are well-fitted by an optically thin (tau(dust)<0.01 in the band) dust shell that is located at about 14 stellar radii with a typical temperature of 700 K and composed of 70% silicate and 30% of amorphous alumina grains. An optically thin (tau(mol)<0.1 in the N band) H2O+SiO molecular shell extending from the photosphere of the star up to 4.4 stellar radii with a typical temperature of 1000 K is added to the model to improve the fit in the 8-9 $\mu$m spectral band. We discuss the probable binary origin of asymmetries as revealed by millimetric observations.

References in corpus (21)

• Correcting for the Effects of Interstellar Extinction
• Self-similarity and scaling behavior of IR emission from radiatively heated dust: I. Theory
• Inverse temperature dependence of the dust submillimeter spectral index
• User Manual for DUSTY
• A Data Exchange Standard for Optical (Visible/IR) Interferometry
• Water in Emission in the ISO Spectrum of the Early M Supergiant Star mu Cephei
• Jets and Tori in Proto-Planetary Nebulae
• Proper-motion binaries in the Hipparcos Catalogue. Comparison with radial velocity data
• Amorphous alumina in the extended atmosphere of Alpha Orionis
• The time variation in infrared water-vapour bands in Mira variables
• The dust disk of HR4049
• The molecular and dusty composition of Betelgeuse's inner circumstellar environment
• Warm water vapor envelope in Mira variables and its effects on the apparent size from the near-infrared to the mid-infrared
• Establishing Visible Interferometer System Responses: Resolved and Unresolved Calibrators
• First VLTI/MIDI observations of a Be star: Alpha Ara
• Circumstellar shells and mass loss rates: Clues to the evolution of S stars
• ISO Mid-Infrared Spectroscopy of Galactic Bulge AGB Stars
• Inverse temperature dependence of the dust submillimeter spectral index
• Infrared Colors and Variability of Evolved Stars from COBE DIRBE Data
• The Henize sample of S stars: IV. New symbiotic stars
• First results from the ESO VLTI Calibrators Program

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