A laboratory approach to the interstellar sulfide dust problem

Begemann, B.; Dorschner, J.; Henning, Th.; Mutschke, H.; Thamm, E.

doi:10.1086/187238

Cited by 116 publications

(126 citation statements)

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“…as proposed by Begemann et al (1994). According to Kimura et al (2005a,b), a MgS (FeS) nucleation from the gas phase produces spherical cubic MgS (FeS) clusters instead of the elongated network-like grains that form when gas-surface reactions are involved in the nucleation process.…”

Section: Summary and Discussionmentioning

confidence: 99%

The inner wind of IRC+10216 revisited: new exotic chemistry and diagnostic for dust condensation in carbon stars

Cherchneff

2012

A&A

119

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Aims. We model the chemistry of the inner wind of the carbon star IRC+10216 and consider the effects of periodic shocks induced by the stellar pulsation on the gas to follow the non-equilibrium chemistry in the shocked gas layers. We consider a very complete set of chemical families, including hydrocarbons and aromatics, hydrides, halogens, and phosphorous-bearing species. Our derived abundances are compared to those for the latest observational data from large surveys and the Herschel telescope. Methods. A semi-analytical formalism based on parameterised fluid equations is used to describe the gas density, velocity, and temperature from 1 R to 5 R . The chemistry is described using a chemical kinetic network of reactions and a set of stiff, ordinary, coupled differential equations is solved. Results. The shocks induce an active non-equilibrium chemistry in the dust formation zone of IRC+10216 where the collision destruction of CO in the post-shock gas triggers the formation of O-bearing species such as H 2 O and SiO. Most of the modelled molecular abundances agree very well with the latest values derived from Herschel data on IRC+10216. The hydrides form a family of abundant species that are expelled into the intermediate envelope. In particular, HF traps all the atomic fluorine in the dust formation zone. The halogens are also abundant and their chemistry is independent of the C/O ratio of the star. Therefore, HCl and other Cl-bearing species should also be present in the inner wind of O-rich AGB or supergiant stars. We identify a specific region ranging from 2.5 R to 4 R , where polycyclic aromatic hydrocarbons form and grow. The estimated carbon dust-to-gas mass ratio derived from the mass of aromatics formed ranges from 1.2 × 10 −3 to 5.8 × 10 −3 and agrees well with existing values deduced from observations. This aromatic formation region is situated outside hot layers where SiC 2 is produced as a bi-product of silicon carbide dust synthesis. The MgS grains can form from the gas phase but in lower quantities than those necessary to reproduce the strength of the 30 μm emission band. Finally, we predict that some molecular lines will show a flux variation with pulsation phase and time (e.g., H 2 O), while other species will not (e.g., CO). These variations merely reflect the non-equilibrium chemistry that destroys and reforms molecules over a pulsation period in the shocked gas of the dust formation zone.

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Section: Summary and Discussionmentioning

confidence: 99%

The inner wind of IRC+10216 revisited: new exotic chemistry and diagnostic for dust condensation in carbon stars

Cherchneff

2012

A&A

119

133

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“…The materials were mixed together using the Bruggeman effective medium theory with the addition of 25% porosity. The refractive-index data were taken from Dorschner et al (1995), Preibisch et al (1993), and Begemann et al (1994) for the pyroxene, carbon, and iron sulfide materials, respectively. To compute the optical properties A23, page 4 of 9 we used the particle shape model from Min et al (2005) with the irregularity parameter f max = 0.8.…”

Section: Model Setupmentioning

confidence: 99%

Imaging the circumstellar environment of the young T Tauri star SU Aurigae

Jeffers

Min

Cánovas

et al. 2013

A&A

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The circumstellar environments of classical T Tauri stars are challenging to directly image because of their high star-to-disk contrast ratio. One method to overcome this is by using imaging polarimetry where scattered and consequently polarised starlight from the star's circumstellar disk can be separated from the unpolarised light of the central star. We present images of the circumstellar environment of SU Aur, a classical T Tauri star at the transition of T Tauri to Herbig stars. The images directly show that the disk extends out to 500 AU with an inclination angle of ∼50 • . Using interpretive models, we derived very small grains in the surface layers of its disk, with a very steep size-and surface-density distribution. Additionally, we resolved a large and extended nebulosity in our images that is most likely a remnant of the prenatal molecular cloud. The position angle of the disk, determined directly from our images, rules out a polar outflow or jet as the cause of this large-scale nebulosity.

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“…Concerning the latter dust species, to our knowledge, there is a major gap in the wavelength range of laboratory measurements. Optical constants are available between 0.3 and 1.1 μm (Egan & Hilgeman 1977) and between 10 and 500 μm (Begemann et al 1994). The Q abs values remain unknown both in the near-IR (rendering the temperature determination uncertain), and in the 5-10 μm range, i.e., in the IRS spectral range.…”

Section: Hd 113766 Amentioning

confidence: 99%

Transient dust in warm debris disks

Olofsson

Juhász

Henning

et al. 2012

A&A

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Context. Debris disks trace remnant reservoirs of leftover planetesimals in planetary systems. In the past years, a handful of "warm" debris disks have been discovered in which emission in excess starts in the mid-infrared. An interesting subset of these warm debris disks shows emission features in mid-infrared spectra, which points towards the presence of μm-sized dust grains, with temperatures above hundreds K. Given the ages of the host stars, the presence of these small grains is puzzling, and raises questions about their origin and survival in time.Aims. This study focuses on determining the mineralogy of the dust around seven debris disks with evidence for warm dust, based on Spitzer/IRS spectroscopic data, to provide new insights into the origin of the dust grains. Methods. We developed and present a new radiative transfer code (Debra) dedicated to spectral energy distribution (SED) modeling of optically thin disks. The Debra code is designed such that it can simultaneously determine dust composition and disk properties. We used this code on the SEDs of seven warm debris disks, in combination with recent laboratory experiments on dust optical properties. Results. We find that most, if not all, debris disks in our sample are experiencing a transient phase, suggesting a production of small dust grains on relatively short timescales. Dust replenishment should be efficient on timescales of months for at least three sources. From a mineralogical point of view, we find that crystalline pyroxene grains (enstatite) have low abundances compared to crystalline olivine grains. The main result of our study is that we find evidence for Fe-rich crystalline olivine grains (Fe/[Mg + Fe] ∼ 0.2) for several debris disks. This finding contrasts with studies of gas-rich protoplanetary disks, where Fe-bearing crystalline grains are usually not observed. Conclusions. These Fe-rich olivine grains, and the overall differences between the mineralogy of dust in Class II disks compared to debris disks suggests that the transient crystalline dust in warm debris disk is of a new generation. We discuss possible crystallization routes to explain our results, and also comment on the mechanisms that may be responsible for the production of small dust grains.

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A laboratory approach to the interstellar sulfide dust problem

Cited by 116 publications

References 0 publications

The inner wind of IRC+10216 revisited: new exotic chemistry and diagnostic for dust condensation in carbon stars

The inner wind of IRC+10216 revisited: new exotic chemistry and diagnostic for dust condensation in carbon stars

Imaging the circumstellar environment of the young T Tauri star SU Aurigae

Transient dust in warm debris disks

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