Mineral formation in stellar winds

Ferrarotti, A. S.; Gail, H. P.

doi:10.1051/0004-6361:20041856

Cited by 24 publications

(18 citation statements)

References 21 publications

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“…Spectral features due to the calcium carbonate phase calcite are observed in certain oxygen-rich stars and planetary nebulae and, unlike naturally occurring carbonates on Earth, cannot be the result of precipitation in aqueous conditions [4][5][6][7]. Furthermore carbonates cannot condense directly from the gas phase on to solid dust particles in O-rich stellar atmospheres because of the low number density of grains in the potential carbonate condensation zone, due to the accelerated outflow of the silicate grains that condense in large quantities closer in to the star [8]. It is the subsequent dry carbonation of the Carich components of these grains, via interaction with gaseous CO 2 at high temperature, that is currently believed to be the most plausible mineralisation pathway for carbonate formation in such environments [9].…”

Section: Introductionmentioning

confidence: 99%

Fine-grained amorphous calcium silicate CaSiO3 from vacuum dried sol–gel – Production, characterisation and thermal behaviour

Thompson

Day

Parker

et al. 2012

Journal of Non-Crystalline Solids

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Section: Introductionmentioning

confidence: 99%

Fine-grained amorphous calcium silicate CaSiO3 from vacuum dried sol–gel – Production, characterisation and thermal behaviour

Thompson

Day

Parker

et al. 2012

Journal of Non-Crystalline Solids

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“…Given that it is unclear how carbonates can form in a circumstellar environment, Ferrarotti & Gail (2005) examined the formation of calcium carbonate in an oxygen-rich stellar wind (C/O < 1) by thermodynamic calculations, assuming the formation of calcite from Ca, H 2 O, and CO. They came to the conclusion that calcite, if at all, would rather form in asymptotic giant branch (AGB) stars with low mass-loss rates (approximately 1 ; 10 À6 M yr À1 ) than in AGB stars in their superwind phase (of which planetary nebulae [ PNs] like NGC 6302 are the remnants however).…”

Section: Introductionmentioning

confidence: 99%

Carbonates in Space: The Challenge of Low‐Temperature Data

Posch¹,

Baier²,

Mutschke³

et al. 2007

ApJ

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Carbonates have repeatedly been discussed as possible carriers of stardust emission bands. However, the band assignments proposed so far were mainly based on room-temperature powder transmission spectra of the respective minerals. Since very cold calcite grains have been claimed to be present in protostars and in planetary nebulae (PNs) such as NGC 6302, the changes of their dielectric functions at low temperatures are relevant from an astronomical point of view. We have derived the infrared optical constants of calcite and dolomite from reflectance spectra, measured at 300, 200, 100, and 10 K, and calculated small-particle spectra for different grain shapes, with the following results. (1) The absorption efficiency factors of both calcite and dolomite are extremely dependent on the particle shapes. This is due to the high peak values of the optical constants of CaCO 3 and CaMg[CO 3 ] 2 . (2) The far-infrared properties of calcite and dolomite also depend very significantly on the temperature. Below 200 K, a pronounced sharpening and increase in the band strengths of the far-infrared resonances occurs. (3) In view of the intrinsic strength and sharpening of the $44 m band of calcite at 200-100 K, the absence of this band, inferred from Infrared Space Observatory data, in PNs requires dust temperatures below 45 K. (4) Calcite grains at such low temperatures can account for the ''92'' m band, while our data rule out dolomite as the carrier of the 60-65 m band. The optical constants presented here are publicly available in the AIU Jena Database of Optical Constants for Cosmic Dust.

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“…These include: the processing of CO 2 -rich ices through catalytic reactions on hydrated silicate surfaces (Ceccarelli et al 2002), direct condensation at high temperatures from gas rich in CaO and CO 2 (Toppani 2005), and solid-gas interaction of silicate grains and hot, gaseous CO 2 (Kemper et al 2002). However, Ferrarotti & Gail (2005) calculated that direct condensation of carbonate grains would not be viable in such environments due to the low temperature (800 K) required for carbonates to precipitate from the gas phase. At distances from the central star implied by these temperatures the outflowing gas would be significantly diluted, suppressing the formation of less stable dust species such as carbonates.…”

Section: Circumstellar Environmentsmentioning

confidence: 99%

Non-aqueous formation of the calcium carbonate polymorph vaterite: astrophysical implications

Day

Thompson

Parker

et al. 2013

A&A

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Aims. We study the formation of calcium carbonate, through the solid-gas interaction of amorphous Ca-silicate with gaseous CO 2 , at elevated pressures, and link this to the possible presence of calcium carbonate in a number of circumstellar and planetary environments. Methods. We use in-situ synchrotron X-ray powder diffraction to obtain detailed structural data pertaining to the formation of the crystalline calcium carbonate phase vaterite and its evolution with temperature. Results. We found that the metastable calcium carbonate phase vaterite was formed alongside calcite, at elevated CO 2 pressure, at room temperature and subsequently remained stable over a large range of temperature and pressure. Conclusions. We report the formation of the calcium carbonate mineral vaterite whilst attempting to simulate carbonate dust grain formation in astrophysical environments. This suggests that vaterite could be a mineral component of carbonate dust and also presents a possible method of formation for vaterite and its polymorphs on planetary surfaces.

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Mineral formation in stellar winds

Cited by 24 publications

References 21 publications

Fine-grained amorphous calcium silicate CaSiO3 from vacuum dried sol–gel – Production, characterisation and thermal behaviour

Fine-grained amorphous calcium silicate CaSiO3 from vacuum dried sol–gel – Production, characterisation and thermal behaviour

Carbonates in Space: The Challenge of Low‐Temperature Data

Non-aqueous formation of the calcium carbonate polymorph vaterite: astrophysical implications

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