Infrared Reflectivity and Raman Scattering of Mg<sub>2</sub>SiO<sub>4</sub> Single Crystal

Servoin, J. L.; Piriou, B.

doi:10.1002/pssb.2220550224

Cited by 164 publications

(114 citation statements)

References 7 publications

Supporting

Mentioning

108

Contrasting

Order By: Relevance

“…Listed are the dust species with their chemical formula, their specific density ρ s , the condensation temperature T cond , the mass fraction of the dust species (given as the mass density of the dust species with respect to the total dust-mass density ρ species /ρ d , assuming all dust species have been formed), and the reference to the optical data for the opacities. The references for the optical constants of the dust species are as follows: 1) de Vries et al (2010) and references therein; 2) Jäger et al (1998); 3) Servoin & Piriou (1973); 4) Henning & Stognienko (1996); 5) Warren (1984); 6) Bertie et al (1969). fractions of crystalline H 2 O ice in the spectra of many sources, in agreement with the large crystalline fraction that we find for OH 127.8+0.0.…”

Section: Thermal Dust Emissionsupporting

confidence: 86%

H₂O vapor excitation in dusty AGB envelopes

Lombaert

Decin

Koter

et al. 2013

A&A

View full text Add to dashboard Cite

Context. AGB stars lose a large percentage of their mass in a dust-driven wind. This creates a circumstellar envelope, which can be studied through thermal dust emission and molecular emission lines. In the case of high mass-loss rates, this study is complicated by the high optical depths and the intricate coupling between gas and dust radiative transfer characteristics. An important aspect of the physics of gas-dust interactions is the strong influence of dust on the excitation of several molecules, including H 2 O. Aims. The dust and gas content of the envelope surrounding the high mass-loss rate OH/IR star OH 127.8+0.0, as traced by Herschel observations, is studied, with a focus on the H 2 O content and the dust-to-gas ratio. We report detecting a large number of H 2 O vapor emission lines up to J = 9 in the Herschel data, for which we present the measured line strengths. Methods. The treatments of both gas and dust species are combined using two numerical radiative transfer codes. The method is illustrated for both low and high mass-loss-rate sources. Specifically, we discuss different ways of assessing the dust-to-gas ratio: 1) from the dust thermal emission spectrum and the CO molecular gas line strengths; 2) from the momentum transfer from dust to gas and the measured gas terminal velocity; and 3) from the determination of the required amount of dust to reproduce H 2 O lines for a given H 2 O vapor abundance. These three diagnostics probe different zones of the outflow, for the first time allowing an investigation of a possible radial dependence of the dust-to-gas ratio. Results. We modeled the infrared continuum and the CO and H 2 O emission lines in OH 127.8+0.0 simultaneously. We find a dustmass-loss rate of (0.5 ± 0.1) × 10 −6 M yr −1 and an H 2 O ice fraction of 16% ± 2% with a crystalline-to-amorphous ratio of 0.8 ± 0.2. The gas temperature structure is modeled with a power law, leading to a constant gas-mass-loss rate between 2 × 10 −5 M yr −1 and 1 × 10 −4 M yr −1 , depending on the temperature profile. In addition, a change in mass-loss rate is needed to explain the J = 1−0 and J = 2−1 CO lines formed in the outer wind, where the older mass-loss rate is estimated to be 1 × 10 −7 M yr −1 . The dust-to-gas ratio found with method 1) is 0.01, accurate to within a factor of three; method 2) yields a lower limit of 0.0005; and method 3) results in an upper limit of 0.005. The H 2 O ice fraction leads to a minimum required H 2 O vapor abundance with respect to H 2 of (1.7 ± 0.2) × 10 −4 . Finally, we report detecting 1612 MHz OH maser pumping channels in the far-infrared at 79.1, 98.7, and 162.9 μm. Conclusions. Abundance predictions for a stellar atmosphere in local thermodynamic equilibrium yield a twice higher H 2 O vapor abundance (∼3 × 10 −4 ), suggesting a 50% freeze-out. This is considerably higher than current freeze-out predictions. Regarding the dust-to-gas ratio, methods 2) and 3) probe a deeper part of the envelope, while method 1) is sensitive to the outermost regions. The latter ...

show abstract

Section: Thermal Dust Emissionsupporting

confidence: 86%

H₂O vapor excitation in dusty AGB envelopes

Lombaert

Decin

Koter

et al. 2013

A&A

View full text Add to dashboard Cite

show abstract

“…For the C23 complex, we build a feature shape index, the S 24 /S 23 flux ratio, computed To better evaluate the relationship between grain size and the C23 shape, we calculate theoretical S 24 /S 23 ratios for synthetic crystalline silicates opacity curves obtained using the Distribution of Hollow Spheres (DHS) method . We consider grains between 0.1 and 2.7 μm in radius, and two different compositions: 100% forsterite (Mg 2 SiO 4 , using optical constants from Servoin & Piriou 1973) and a mixture composed of 50% forsterite plus 50% enstatite (MgSiO 3 , optical constants taken from Jaeger et al 1998). Grains larger than ∼3.0 μm, for either enstatite or forsterite, do not give striking results, as the feature disappears into the continuum.…”

Section: Growth Of Cold Crystalline Silicatesmentioning

confidence: 99%

“…We consider amorphous species that include silicates of olivine stoichiometry (glassy MgFeSiO 4 , optical constants from Dorschner et al 1995), and silicates of pyroxene stoichiometry (glassy MgFeSi 2 O 6 , optical constants from Dorschner et al 1995). For the crystalline species, we use enstatite (MgSiO 3 ) optical constants from Jaeger et al (1998) and forsterite (Mg 2 SiO 4 ) optical constants from Servoin & Piriou (1973). Theoretical mass opacities κ λ are computed using Mie theory (valid for hard spheres) for the amorphous species and DHS theory (Distribution of Hollow Spheres, Min et al 2005) for the crystalline silicates.…”

Section: Degree Of Crystallinity Of the Warm Versus Cold Disk Regionsmentioning

confidence: 99%

C2D Spitzer-IRS spectra of disks around T Tauri stars

Olofsson¹,

Augereau²,

Dishoeck

et al. 2009

A&A

103

148

View full text Add to dashboard Cite

Aims. Dust grains in the planet-forming regions around young stars are expected to be heavily processed due to coagulation, fragmentation, and crystallization. This paper focuses on the crystalline silicate dust grains in protoplanetary disks for a statistically significant number of TTauri stars (96). Methods. As part of the cores to disks (c2d) legacy program, we obtained more than a hundred Spitzer/IRS spectra of TTauri stars, over a spectral range of 5−35 μm where many silicate amorphous and crystalline solid-state features are present. At these wavelengths, observations probe the upper layers of accretion disks up to distances of a dozen AU from the central object.Results. More than 3/4 of our objects show at least one crystalline silicate emission feature that can be essentially attributed to Mg-rich silicates. The Fe-rich crystalline silicates are largely absent in the c2d IRS spectra. The strength and detection frequency of the crystalline features seen at λ > 20 μm correlate with each other, while they are largely uncorrelated with the observational properties of the amorphous silicate 10 μm feature. This supports the idea that the IRS spectra essentially probe two independent disk regions: a warm zone (≤1 AU) emitting at λ ∼ 10 μm and a much colder region emitting at λ > 20 μm (≤10 AU). We identify a crystallinity paradox, as the long-wavelength (λ > 20 μm) crystalline silicate features are detected 3.5 times more frequently (∼55% vs. ∼15%) than the crystalline features arising from much warmer disk regions (λ ∼ 10 μm). This suggests that the disk has an inhomogeneous dust composition within ∼10 AU. The analysis of the shape and strength of both the amorphous 10 μm feature and the crystalline feature around 23 μm provides evidence for the prevalence of μm-sized (amorphous and crystalline) grains in upper layers of disks. Conclusions. The abundant crystalline silicates found far from their presumed formation regions suggest efficient outward radial transport mechanisms in the disks around TTauri stars. The presence of μm-sized grains in disk atmospheres, despite the short timescales for settling to the midplane, suggests efficient (turbulent) vertical diffusion, probably accompanied by grain-grain fragmentation to balance the expected efficient growth. In this scenario, the depletion of submicron-sized grains in the upper layers of the disks points toward removal mechanisms such as stellar winds or radiation pressure.

show abstract

“…The amorphous species include silicates of olivine stoichiometry (glassy MgFeSiO 4 , density of 3.71 g cm −3 , optical indexes from Dorschner et al 1995), silicates of pyroxene stoichiometry (glassy MgFeSiO 6 , density of 3.2 g cm −3 , Dorschner et al 1995), and silica (amorphous quartz, density of 3.33 g cm −3 , Henning & Mutschke 1997). For the Mg-rich (see Olofsson et al 2009) crystalline species, we consider enstatite (MgSiO 3 , density of 2.8 g cm −3 , Jaeger et al 1998) and forsterite (Mg 2 SiO 4 , density of 2.6 g cm −3 , Servoin & Piriou 1973).…”

Section: Theoretical Opacities and Grain Sizesmentioning

confidence: 99%

C2D Spitzer-IRS spectra of disks around T Tauri stars

Olofsson¹,

Augereau²,

Dishoeck

et al. 2010

A&A

View full text Add to dashboard Cite

Context. Dust particles evolve in size and lattice structure in protoplanetary disks, due to coagulation, fragmentation and crystallization, and are radially and vertically mixed in disks due to turbulent diffusion and wind/radiation pressure forces. Aims. This paper aims at determining the mineralogical composition and size distribution of the dust grains in planet forming regions of disks around a statistical sample of 58 T Tauri stars observed with Spitzer/IRS as part of the Cores to Disks (c2d) Legacy Program. Methods. We present a spectral decomposition model, named "B2C", that reproduces the IRS spectra over the full spectral range (5-35 μm). The model assumes two dust populations: a warm component responsible for the 10 μm emission arising from the disk inner regions ( 1 AU) and a colder component responsible for the 20-30 μm emission, arising from more distant regions ( 10 AU). The fitting strategy relies on a random exploration of parameter space coupled with a Bayesian inference method. Results. We show evidence for a significant size distribution flattening in the atmospheres of disks compared to the typical MRN distribution, providing an explanation for the usual flat, boxy 10 μm feature profile generally observed in T Tauri star spectra. We reexamine the crystallinity paradox, observationally identified by Olofsson et al. (2009, A&A, 507, 327), and we find a simultaneous enrichment of the crystallinity in both the warm and cold regions, while grain sizes in both components are uncorrelated. We show that flat disks tend to have larger grains than flared disk. Finally our modeling results do not show evidence for any correlations between the crystallinity and either the star spectral type, or the X-ray luminosity (for a subset of the sample). Conclusions. The size distribution flattening may suggests that grain coagulation is a slightly more effective process than fragmentation (helped by turbulent diffusion) in disk atmospheres, and that this imbalance may last over most of the T Tauri phase. This result may also point toward small grain depletion via strong stellar winds or radiation pressure in the upper layers of disk. The non negligible cold crystallinity fractions suggests efficient radial mixing processes in order to distribute crystalline grains at large distances from the central object, along with possible nebular shocks in outer regions of disks that can thermally anneal amorphous grains.

show abstract

Infrared Reflectivity and Raman Scattering of Mg₂SiO₄ Single Crystal

Cited by 164 publications

References 7 publications

H₂O vapor excitation in dusty AGB envelopes

H₂O vapor excitation in dusty AGB envelopes

C2D Spitzer-IRS spectra of disks around T Tauri stars

C2D Spitzer-IRS spectra of disks around T Tauri stars

Contact Info

Product

Resources

About

Infrared Reflectivity and Raman Scattering of Mg2SiO4 Single Crystal

Cited by 164 publications

References 7 publications

H2O vapor excitation in dusty AGB envelopes

H2O vapor excitation in dusty AGB envelopes

C2D Spitzer-IRS spectra of disks around T Tauri stars

C2D Spitzer-IRS spectra of disks around T Tauri stars

Contact Info

Product

Resources

About

Infrared Reflectivity and Raman Scattering of Mg₂SiO₄ Single Crystal

H₂O vapor excitation in dusty AGB envelopes

H₂O vapor excitation in dusty AGB envelopes