Non-stoichiometric amorphous magnesium-iron silicates in circumstellar dust shells. Dust growth in outflows from supergiants

Abstract

We investigate the dust growth in oxygen-rich stellar outflows for a set of nine well-observed massive supergiants with optically thin dust shells. Models of the infrared emission from their circumstellar dust shells are compared to their observed infrared spectra so as to derive the essential parameters that govern dust formation in the extended envelope of these stars. The results obtained from the comparative study are also compared with the predictions of a model for silicate dust condensation solely based on laboratory data and basic stellar properties. The infrared emission in the wavelength range between 6 and 25 mu can be reproduced rather well by a mixture of non-stoichiometric iron-bearing silicates, alumina, and metallic iron dust particles for all nine objects. The observed spectra obtained from three objects, mu Cep, RW Cyg, and RS Per, can be reproduced by a stationary and (essentially) spherically symmetric outflow which enables a direct comparison with predictions from a theoretical dust growth model. The temperature at the onset of massive silicate dust growth is of the order of 920 K and the corresponding outflow velocity of the order of the sound velocity for these objects. The condensation temperature suggests that the silicate dust grows on the corundum dust grains that are formed well in the interior of the silicate dust shell at a much higher temperature. Our results propose that regarding the two major problems of dust formation in stellar outflows: (i) formation of seed nuclei; (ii) their growth to macroscopic dust grains, we are gradually coming close to a quantitative understanding of the second item.

arXiv comment29 pages, 9 figures, accepted by Astronomy & Astrophysics

References in corpus (38)

• Grids of stellar models with rotation - I. Models from 0.8 to 120 Msun at solar metallicity (Z = 0.014)
• Mass Loss: Its Effect on the Evolution and Fate of High-Mass Stars
• The Effective Temperature Scale of Galactic Red Supergiants: Cool, But Not As Cool As We Thought
• Present-day cosmic abundances. A comprehensive study of nearby early B-type stars and implications for stellar and Galactic evolution and interstellar dust models
• Modeling optical properties of cosmic dust grains using a distribution of hollow spheres
• The mass-loss rates of red supergiants and the de Jager prescription
• Dust formation in the oxygen-rich AGB star IK Tau
• The shape and composition of interstellar silicate grains
• Variability in red supergiant stars: pulsations, long secondary periods and convection noise
• A new mass-loss rate prescription for red supergiants
• Atmospheric dynamics and the mass loss process in red supergiant stars
• The dust condensation sequence in red super-giant stars
• Radiative hydrodynamics simulations of red supergiant stars: I. interpretation of interferometric observations
• Coordinated Analyses of Presolar Grains in the Allan Hills 77307 and Queen Elizabeth Range 99177 Meteorites
• Effective medium theories for irregular fluffy structures: aggregation of small particles
• Radiative hydrodynamics simulations of red supergiant stars: II. simulations of convection on Betelgeuse match interferometric observations
• Radiative hydrodynamics simulations of red supergiant stars. IV gray versus non-gray opacities
• Classification of 2.4-45.2 Micron Spectra from the ISO Short Wavelength Spectrometer
• New insights into the dust formation of oxygen-rich AGB stars
• Evolutionary tracks for Betelgeuse
• Seed particle formation for silicate dust condensation by SiO nucleation
• VLTI/AMBER spectro-interferometric imaging of VX Sgr's inhomogenous outer atmosphere
• Amorphous alumina in the extended atmosphere of Alpha Orionis
• Large dust grains in the wind of VY Canis Majoris
• The molecular and dusty composition of Betelgeuse's inner circumstellar environment
• Properties of the CO and H${}_2$O MOLsphere of the red supergiant Betelgeuse from VLTI/AMBER observations
• Supergiant Temperatures and Linear Radii from Near-Infrared Interferometry
• On the metallicity dependence of crystalline silicates in oxygen-rich asymptotic giant branch stars and red supergiants
• Infrared Spectra and Visibilities as Probes of the Outer Atmospheres of Red Supergiant Stars
• Morphological effects on IR band profiles: Experimental spectroscopic analysis with application to observed spectra of oxygen-rich AGB stars
• TEXES Observations of M Supergiants: Dynamics and Thermodynamics of Wind Acceleration
• NOEMA maps the CO $J=2-1$ environment of the red supergiant $\mu$ Cep
• The Antares emission nebula and mass loss of alpha Sco A
• The inner dust shell of Betelgeuse detected by polarimetric aperture-masking interferometry
• ALMA and VLA reveal the lukewarm chromospheres of the nearby red supergiants Antares and Betelgeuse
• High spectral resolution spectroscopy of the SiO fundamental lines in red giants and red supergiants with VLT/VISIR
• A hydrodynamic study of the circumstellar envelope of alpha Scorpii
• Optical properties of non-stoichiometric amorphous silicates with application to circumstellar dust extinction