Mineral formation in stellar winds

During the final stages of their evolution, stars with low to intermediate masses produce huge quantities -up to the order of earth masses per yearof dust grains. This production of solid particles is of crucial importance both for the physico-chemical conditions in the respective circumstellar environments and for the cosmic cycle of matter.The branch of astronomy dealing with cosmic dust -sometimes referred to as solid state astropyhsics -uses three principal methods: astronomical infrared spectroscopy, laboratory measurements of optical properties of solids and modelling the chemical and physical processes going on in the atmospheres of evolved stars.Considerable progress has been achieved, during the past decade, in solid state astropyhsics; specific questions have arisen which necessitate new, dedicated measurements and observations. Here we highlight some aspects of this progress and then proceed to outlining insights in this field which are about to be attained by means of new satellite facilities such as Spitzer and Herschel.

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“…5). This identification is plausible also on the basis of the predictions from condensation theory made by Ferrarotti & Gail (2003).…”

Section: The 195 Micron Bandsupporting

confidence: 53%

Progress and Perspectives in Solid State Astrophysics from ISO to Herschel

Posch

Mutschke

Kerschbaum

et al. 2006

Reviews in Modern Astronomy

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“…Further on in the wind, at lower temperatures, these grains can be the seeds for the formation of enstatite, forsterite and the amorphous silicates we observe in many AGB stars. (this scenario was proposed and adapted by Grossman & Larimer 1974;Onaka et al 1989;Tielens 1990;Cami 2002 the magnesium-rich oxides can form at higher temperatures (up to 1200 K) due to the reaction of H 2 O with atomic magnesium (Ferrarotti & Gail 2003). The broad picture for C-type AGB stars is simpler, but some key details have yet to be filled in.…”

Section: Dust Formation In Agb Starsmentioning

confidence: 98%

TheSpitzerspectroscopic survey of S-type stars

Smolders

Neyskens

Blommaert

et al. 2012

A&A

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Context. S-type AGB stars are thought to be in the transitional phase between M-type and C-type AGB stars. Because the composition of the circumstellar environment reflects the photospheric abundances, one may expect a strong influence of the stellar C/O ratio on the molecular chemistry and the mineralogy of the circumstellar dust. Aims. In this paper, we present a large sample of 87 intrinsic galactic S-type AGB stars, observed at infrared wavelengths with the Spitzer Space Telescope, and supplemented with ground-based optical data. Methods. On the one hand, we derive the stellar parameters from the optical spectroscopy and photometry, using a grid of model atmospheres. On the other, we decompose the infrared spectra to quantify the flux-contributions from the different dust species. Finally, we compare the independently determined stellar parameters and dust properties. Results. For the stars without significant dust emission features, we detect a strict relation between the presence of SiS absorption in the Spitzer spectra and the C/O ratio of the stellar atmosphere. These absorption bands can thus be used as an additional diagnostic for the C/O ratio. For stars with significant dust emission, we define three distinct groups, based on the relative contribution of certain dust species to the infrared flux. We find a strong link between group-membership and C/O ratio. Furthermore, we show that these groups can be explained by assuming that the dust-condensation can be cut short before silicates are produced, while the remaining free atoms and molecules can then be used to form the observed magnesium sulfides or the carriers of the unidentified 13 µm and 20 µm features. Finally, we present the detection of emission features attributed to molecules and dust characteristic to C-type stars, such as molecular SiS, hydrocarbons and magnesium sulfide grains. We show that we often detect magnesium sulfides together with molecular SiS and we propose that it is formed by a reaction of SiS molecules with Mg.

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“…In the model calculations we assume n d = 3 × 10 −13 · N H for all dust species (see Ferrarotti & Gail 2003), where N H is the number of hydrogen nuclei, which is determined from the mass density ρ by…”

Section: Degree Of Condensationmentioning

confidence: 99%

Composition and quantities of dust produced by AGB-stars and returned to the interstellar medium

Ferrarotti¹,

Gail²

2006

A&A

Self Cite

321

510

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The composition of the dust mixture and the amounts of dust returned into the interstellar medium during the evolution of low and intermediate mass stars on the AGB is calculated by simple models for dust-forming stellar winds with M-, S-, and C-star chemistry. These models consider the most abundant dust species formed in circumstellar dust shells, i.e. olivine-and pyroxene-type silicate grains and iron grains in the case of M-stars, iron grains in the case of S-stars, and carbon, SiC, and iron grains in the case of C-stars. The wind models are combined with calculations of synthetic AGB-evolution to consistently determine the variation of the dust injection rate into the interstellar medium from AGB-stars with initial mass and metallicity as the stars evolve along the AGB and change their chemical surface compositions due to repeated "dredge-up" episodes. Numerical results are presented for initial stellar masses from 1 to 7 M and for metallicities between Z = 0.001 and Z = 0.04, which can then be used to calculate chemical evolution models for the dust content of galaxies.

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Mineral formation in stellar winds

Cited by 24 publications

References 23 publications

Progress and Perspectives in Solid State Astrophysics from ISO to Herschel

Progress and Perspectives in Solid State Astrophysics from ISO to Herschel

TheSpitzerspectroscopic survey of S-type stars

Composition and quantities of dust produced by AGB-stars and returned to the interstellar medium

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