AN INVESTIGATION INTO THE ORIGIN OF Fe-RICH PRESOLAR SILICATES IN ACFER 094

Bose, Maitrayee; Floss, C.; Stadermann, F. J.

doi:10.1088/0004-637x/714/2/1624

Cited by 60 publications

(74 citation statements)

References 63 publications

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“…Since the detection by Nguyen & Zinner (2004) that also silicates from stellar sources are present in meteorites it has become possible also to analyze presolar silicate dust grains. Vollmer et al (2009), Bose et al (2010), Nguyen et al (2010), and Bose et al (2012) have provided direct information on the size and composition for 145 such presolar silicate grains.…”

Section: Silicate Stardustmentioning

confidence: 99%

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Optical Properties of Non-stoichiometric Amorphous Silicates with Application to Circumstellar Dust Extinction

Tamanai

Pucci

Dohmen

et al. 2017

ApJ

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We determine the optical constants of non-stoichiometric amorphous magnesium-iron silicates and demonstrate that these can well reproduce the observed mid-infrared emission spectra of evolved stars. Stoichiometric and non-stoichiometric amorphous magnesium-iron silicate films are fabricated by pulsed laser deposition. Transmittance and ellipsometry measurements are performed in the wavelength range between 2 and 200 µm and 1.7 and 33 µm, respectively. Optical constants are derived from transmittance and ellipsometric Ψ and ∆ spectra by means of oscillator models. These newly obtained optical constants are applied in radiative transfer models for examining reproducibility of the observed spectral features of circumstellar dust shells around supergiants. The spectra of four selected supergiants are dominated by amorphous silicate dust emission in the wavelength range of 9 and 25 µm. To obtain a good fit to the observed spectra, we take into account amorphous corundum and metallic iron particles as additional dust components to the model calculations to rationalize the dust emission at λ < 8 µm. For each of the objects, a set of model parameters (dust mass, condensation temperature) is derived by an automated optimization procedure which well reproduces the observation. Consequently, our model spectra using new optical data find that the silicate bands at ∼ 10 and ∼ 18 µm depend on the magnesium and iron ratio in the silicate system, and that a good fit requires a significant iron content of the amorphous silicate dust component to reproduce the observed peak positions and shape of the silicate bands.

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Section: Silicate Stardustmentioning

confidence: 99%

“…The relative abundances of the components are determined by a least square minimization such that the relative Bose et al (2010). The red diamonds refer to the synthetic amorphous silicates studied in this paper (see Table 1).…”

Section: Silicate Stardustmentioning

confidence: 99%

Optical Properties of Non-stoichiometric Amorphous Silicates with Application to Circumstellar Dust Extinction

Tamanai

Pucci

Dohmen

et al. 2017

ApJ

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“…We consider, for simplicity, only the formation of a single amorphous silicate dust component. An iron-rich composition is assumed since presolar silicate grains from AGB stars have significant iron contents (Vollmer et al 2009;Nguyen et al 2010;Bose et al 2010) and are only iron poor rarely. The dust opacity required for calculating the radiation pressure is calculated with the complex index of refraction of the dirty silicate model of Ossenkopf et al (1992, their set 1).…”

Section: Ballistic Modelmentioning

confidence: 99%

“…In case of late-type M stars, one observes that the dominating dust components formed in the outflow are magnesium-iron-silicates (see Molster et al 2010, for a review on observations). Laboratory investigations of presolar silicate dust grains from asymptotic giant branch (AGB) stars have shown that usually Mg-Fe-silicates are formed (Vollmer et al 2009;Nguyen et al 2010;Bose et al 2010), which have widely varying iron content where iron-poor grains are rare.…”

Section: Introductionmentioning

confidence: 99%

Silicate condensation in Mira variables

Gail

Scholz

Pucci

2016

A&A

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Context. The formation of dust in winds of cool and highly evolved stars and the rate of injection of dust into the interstellar medium is not yet completely understood, despite the importance of the process for the evolution of stars and galaxies. This holds in particular for oxygen-rich stars, where it is still not known which process is responsible for the formation of the necessary seed particles of their silicate dust. Aims. We study whether the condensation of silicate dust in Mira envelopes could be caused by cluster formation by the abundant SiO molecules. Methods. We solve the dust nucleation and growth equations in the co-moving frame of a fixed mass element for a simplified model of the pulsational motions of matter in the outer layers of a Mira variable, which is guided by a numerical model for Mira pulsations. It is assumed that seed particles form through the clustering of SiO. The calculation of the nucleation rate is based on published experimental data. The quantity of dust formed is calculated via a moment method and the calculation of radiation pressure on dusty gas is based on a dirty silicate model. Results. Dust nucleation occurs in the model at the upper culmination of the trajectory of a gas parcel where it stays for a considerable time at low temperatures. Subsequent dust growth occurs during the descending part of the motion and continues after the next shock reversed motion. It is found that sufficient dust forms that radiation pressure exceeds the gravitational pull of the stars such that the mass element is finally driven out of the star. Conclusions. Nucleation of dust particles by clustering of the abundant SiO molecules could be the mechanism that triggers silicate dust formation in Miras.

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“…1a). Though there seems to be no immediately obvious reason why this should be different for the tiny grains condensed in a circumstellar shell and for nanometre-sized laboratory condensed grains, there are indications from presolar silicate dust grains that there are noticeable deviations from sphericity (Vollmer et al 2009;Bose et al 2010). Therefore we also use the continuous distribution of ellipsoids (see, e.g., Bohren & Huffman 1983), in order to account for possible non-sphericity effects.…”

Section: Opacitymentioning

confidence: 99%

Laboratory measurement of optical constants of solid SiO and application to circumstellar dust

Wetzel

Klevenz

Gail

et al. 2013

A&A

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Context. Silicate minerals belong to the most abundant solids that form in cosmic environments. Their formation requires that a sufficient number of oxygen atoms per silicon atom are freely available. For the standard cosmic element mixture this can usually be taken for granted, but it becomes a problem at the transition from the oxygen-rich chemistry of M-stars to the carbon-rich chemistry of C-stars. In the intermediate type S-stars, most of the oxygen and carbon is consumed by formation of CO and SiO molecules, and left-over oxygen to build SiO 4 -tetrahedrons in solids becomes scarce. Under such conditions SiO molecules from the gas phase may condense into solid SiO. The infrared absorption spectrum of solid SiO differs from that of normal silicates by the absence of Si-O-Si bending modes around 18 μm whereas the absorption band due to Si-O bond stretching modes at about 10 μm is present. Observations show that exactly this particular characteristic can be found in some S-star spectra. Aims. We demonstrate that this observation may be explained by the formation of solid SiO as a major dust component at C/O abundance ratios close to unity. Methods. The infrared absorption properties of solid SiO are determined by laboratory transmission measurements of thin films of SiO produced by vapour deposition on a Si(111) wafer in the range between 100 cm −1 and 5000 cm −1 (2 μm and 100 μm). From the measured spectra the dielectric function of SiO is derived by using a Brendel-oscillator model, particularly suited to the representation of optical properties of amorphous materials. The results are used in model calculations of radiative transfer in circumstellar dust shells with solid SiO dust in order to determine the spectral features due to SiO dust. Results. Comparison of synthetic and observed spectra shows that reasonable agreement is obtained between the main spectral characteristics of emission bands due to solid silicon monoxide and an emission band centred on 10 μm, but without the accompanying 18μm band, observed in some S-stars. We propose that solid SiO is the carrier material of this 10 μm spectral feature.

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AN INVESTIGATION INTO THE ORIGIN OF Fe-RICH PRESOLAR SILICATES IN ACFER 094

Cited by 60 publications

References 63 publications

Optical Properties of Non-stoichiometric Amorphous Silicates with Application to Circumstellar Dust Extinction

Optical Properties of Non-stoichiometric Amorphous Silicates with Application to Circumstellar Dust Extinction

Silicate condensation in Mira variables

Laboratory measurement of optical constants of solid SiO and application to circumstellar dust

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