Morphological effects on IR band profiles

Tamanai, Akemi; Mutschke, H.; Blum, Jürgen; Posch, Th.; Koike, C.; Ferguson, Jason W.

doi:10.1051/0004-6361/200911614

Cited by 33 publications

(35 citation statements)

References 78 publications

(121 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This underlines the extreme importance of laboratory experiments to improve our understanding of cosmic dust properties. The aerosol technique is a promising technique that provide direct measurements of optical properties, with as little environmental contamination as possible (e.g., Tamanai et al 2009). 6.…”

Section: Resultsmentioning

confidence: 99%

“…As mentioned previously, these efficiencies suffer from uncertainties at different levels. Laboratory measurements are unfortunately subject to various environmental effects such as electromagnetic polarization of the embedding medium (KBr, CsI or PE) when using the pellet technique (see Tamanai et al 2006Tamanai et al , 2009. Additionally, when using the optical constant, scattering theories have their own caveats, as discussed for example in Min et al (2007) for the Mie and DHS theories.…”

Section: Forsterite and Crystalline Olivine Grainsmentioning

confidence: 99%

See 1 more Smart Citation

Transient dust in warm debris disks

Olofsson

Juhász

Henning

et al. 2012

A&A

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Forsterite and Crystalline Olivine Grainsmentioning

confidence: 99%

Transient dust in warm debris disks

Olofsson

Juhász

Henning

et al. 2012

A&A

Self Cite

View full text Add to dashboard Cite

show abstract

“…In general, one of the particulates can be characterized by a roundish shape or at least by having round edges, which is often the case for particles that have been condensed from the gas or liquid phase in a relatively fast process, whereas the other particulate is characterized by an irregular grain shape with sharp edges, which is typical of particulates produced by crushing larger pieces of material, but may also result from slow crystal growth. The spectra of the two classes of particulates differ significantly, as discussed by Tamanai et al (2006bTamanai et al ( , 2009b. Correspondence with astronomically observed infrared dust emission bands has been found to be better in some cases for the roundish shapes, especially for the oxides in AGB star outflows (Tamanai et al 2009b; see also Posch et al 1999;and Fabian et al 2001a), but in other cases better for the irregular shapes, especially for forsterite (Tamanai et al 2006b; see also Molster et al 2002;Fabian et al 2001b).…”

Section: Experimental Spectramentioning

confidence: 90%

“…Detailed analyses of, e.g., Spitzer IRS, and ground-based mid-infrared spectra including interferometric data (VLTI/MIDI) have been published in the last years for dust emission from accretion disks (e.g. van Boekel et al 2004), debris disks (e.g. Lisse et al 2007), and comets (e.g.…”

Section: Introductionmentioning

confidence: 99%

Laboratory-based grain-shape models for simulating dust infrared spectra

Mutschke¹,

Min

Tamanai³

2009

A&A

Self Cite

View full text Add to dashboard Cite

Context. Analysis of thermal dust emission spectra for dust mineralogy and physical grain properties depends on comparison spectra, which are either laboratory-measured infrared extinction spectra or calculated extinction cross sections based on certain grain models. Often, the agreement between these two kinds of spectra, if available, is not yet satisfactory because of the strong influence of the grain morphology on the spectra. Aims. We investigate the ability of the statistical light-scattering model with a distribution of form factors (DFF) to reproduce measured infrared dust extinction spectra for particles that are small compared to the wavelength, i.e. in the size range of 1 μm and smaller. Methods. We take advantage of new experimental spectra measured for free particles dispersed in air with accompanying information on the grain morphology. For the calculations, we used DFFs that were derived for aggregates of spherical grains, as well as for compact grain shapes corresponding to Gaussian random spheres. In addition we used a fitting algorithm to obtain the best-fit DFFs for the various laboratory samples. In this way we can independently derive information on the shape of the grains from their infrared spectra. Results. With the DFF model, we achieve an adequate fit of the experimental IR spectra. The differences in the IR band profiles between the spectra of particulates with different grain shapes are simply reflected by different DFFs. Irregular particle shapes require a DFF similar to that of a Gaussian Random Sphere with σ = 0.3, whereas roundish grain shapes are best fitted with that of a fractal aggregate of D f = 2.4-1.8. The fitted DFFs generally reproduce the measured spectral shapes quite well. For anisotropic materials, different DFFs are needed for the different crystallographic axes. The implications of this finding are discussed. Conclusions. The use of this model could be a step forward toward more realistic comparison data in infrared spectral analysis of thermal dust emission spectra, provided that these spectra are dominated by emission from submicron grains.

show abstract

“…As for the term "sapphire", we will avoid it in the following, since it refers to α- Nittler 1997;Clayton & Nittler 2004;Hoppe 2004). However, it has so far not been possible to set any strong constrain on the polytype of Al 2 O 3 by presolar grain studies (which is a problem, since many polytypes of Al 2 O 3 exist -see, e.g., Tamanai et al 2009). Until very recently, it has been impossible to produce any satisfying fit of the 13 μm band using optical constants of corundum at room temperature.…”

Section: Hot Corundum and The 13 μM Bandmentioning

confidence: 99%

Optical constants of refractory oxides at high temperatures

Zeidler

Posch

Mutschke

2013

A&A

Self Cite

View full text Add to dashboard Cite

Context. Many cosmic dust species, among them refractory oxides, form at temperatures higher than 300 K. Nevertheless, most astrophysical studies are based on the room-temperature optical constants of solids, such as corundum and spinel. A more realistic approach is needed for these materials, especially in the context of modeling late-type stars. Aims. We aimed at deriving sets of optical constants of selected, astrophysically relevant oxide dust species with high melting points. Methods. A high-temperature, high-pressure cell and a Fourier-transform spectrometer were used to measure reflectance spectra of polished samples. For corundum (α-Al 2 O 3 ), spinel (MgAl 2 O 4 ), and α-quartz (SiO 2 ), temperature-dependent optical constants were measured from 300 K up to more than 900 K. Small particle spectra were also calculated from these data. Results. All three examined oxides show a significant temperature dependence of their mid-IR bands. For the case of corundum, we find that the 13 μm emission feature -seen in the IR spectra of many AGB stars -can very well be assigned to this mineral species. The best fit of the feature is achieved with oblate corundum grains at (mean) temperatures around 550 K. Spinel remains a viable carrier of the 13 μ feature as well, but only for T < 300 K and nearly spherical grain shapes. Under such circumstances, spinel grains may also account for the 31.8 μm band that is frequently seen in sources of the 13 μm feature and which has not yet been identified with certainty.

show abstract

Morphological effects on IR band profiles

Cited by 33 publications

References 78 publications

Transient dust in warm debris disks

Transient dust in warm debris disks

Laboratory-based grain-shape models for simulating dust infrared spectra

Optical constants of refractory oxides at high temperatures

Contact Info

Product

Resources

About