Dust and molecular shells in asymptotic giant branch stars - Mid-infrared interferometric observations of R Aql, R Aqr, R Hya, W Hya and V Hya

Abstract

Mid-IR (8 - 13 micron) interferometric data of four oxygen-rich AGB stars (R Aql, R Aqr, R Hya, and W Hya) and one carbon-rich AGB star (V Hya) were obtained with MIDI/VLTI between April 2007 and September 2009. The spectrally dispersed visibility data are analyzed by fitting a circular fully limb-darkened disk (FDD). Results. The FDD diameter as function of wavelength is similar for all oxygen-rich stars. The apparent size is almost constant between 8 and 10 micron and gradually increases at wavelengths longer than 10 micron. The apparent FDD diameter in the carbon-rich star V Hya essentially decreases from 8 to 12 micron. The FDD diameters are about 2.2 times larger than the photospheric diameters estimated from K-band observations found in the literature. The silicate dust shells of R Aql, R Hya and W Hya are located fairly far away from the star, while the silicate dust shell of R Aqr and the amorphous carbon (AMC) and SiC dust shell of V Hya are found to be closer to the star at around 8 photospheric radii. Phase-to-phase variations of the diameters of the oxygen-rich stars could be measured and are on the order of 15% but with large uncertainties. From a comparison of the diameter trend with the trends in RR Sco and S Ori it can be concluded that in oxygen-rich stars the overall larger diameter originates from a warm molecular layer of H2O, and the gradual increase longward of 10 micron can be most likely attributed to the contribution of a close Al2O3 dust shell. The chromatic trend of the Gaussian FWHM in V Hya can be explained with the presence of AMC and SiC dust. The observations suggest that the formation of amorphous Al2O3 in oxygen- rich stars occurs mainly around or after visual minimum. However, no firm conclusions can be drawn concerning the mass-loss mechanism.

32 pages (including 7 pages appendix), 10 figures

References in corpus (22)

• Too little radiation pressure on dust in the winds of oxygen-rich AGB stars
• A close halo of large transparent grains around extreme red giant stars
• The dust condensation sequence in red super-giant stars
• 2D Models for Dust-driven AGB Star Winds
• The Mira variable S Ori: Relationships between the photosphere, molecular layer, dust shell, and SiO maser shell at 4 epochs
• Dust-driven Winds and Mass Loss of C-rich AGB Stars with subsolar Metallicities
• Dynamical Opacity-Sampling Models of Mira Variables. II: Time-Dependent Atmospheric Structure and Observable Properties of 4 M-Type Model Series
• Winds of M- and S-type AGB stars: an unorthodox suggestion for the driving mechanism
• Tracing the development of dust around evolved stars: The case of 47 Tuc
• The molecular and dusty composition of Betelgeuse's inner circumstellar environment
• The Keck Aperture Masking Experiment: Multi-Wavelength Observations of 6 Mira Variables
• The spectroscopic orbit and the geometry of R Aqr
• Detached shells as tracers of AGB-ISM bow shocks
• First Images of R Aquarii and its Asymmetric H${}_2$O Shell
• Outer jet X-ray and radio emission in R Aquarii: 1999.8 to 2004.0
• Dust driven mass loss from carbon stars as function of stellar parameters - II. Effects of grain size on wind properties
• ISO Mid-Infrared Spectroscopy of Galactic Bulge AGB Stars
• Temporal variations of the outer atmosphere and the dust shell of the carbon-rich Mira variable V Oph probed with VLTI/MIDI
• The mid-infrared diameter of W Hydrae
• Search for radiative pumping lines of OH masers: I. The 34.6um absorption line towards 1612 MHz OH maser sources
• Distribution and kinematics of the HCN(3-2) emission down to the innermost region in the envelope of the O-rich star W Hya
• Silicates in D-type symbiotic stars: an ISO overview

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• Inner dusty envelope of the AGB stars W~Hydrae, SW\,Virginis, and R~Crateris using SPHERE/ZIMPOL
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• The Isaac Newton Telescope monitoring survey of Local Group dwarf galaxies -- IV. The star formation history of Andromeda VII derived from long period variable stars
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• Atomium: The astounding complexity of the near circumstellar environment of the M-type AGB star R Hydrae. I. Morpho-kinematical interpretation of CO and SiO emission
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• Locating dust and molecules in the inner circumstellar environment of R~Sculptoris with MATISSE
• Asymmetries in asymptotic giant branch stars and their winds. I. From 3D RHD models to synthetic observables
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