Infrared reflection spectra of forsterite crystal

Abstract

Polarized infrared reflectance of large single crystals of forsterite was measured for each crystal axis at frequencies between 5000 cm −1 and 100 cm −1 with a resolution of 1 cm −1 . The reflectance spectra were analyzed based on classical dispersion theory. A set of oscillator parameters for crystalline axes of forsterite was obtained. Those parameters are used to derive optical constants of forsterite, which are important for analyses of observed spectra of astronomical objects and laboratory spectra of particle samples. Calculations of absorption for small particles using the bulk optical constants are compared with mid-infrared and far-infrared absorption spectra measured in the laboratory.

Transient dust in warm debris disks

“…Figure 2 shows several laboratory measurements for two wavelength ranges. From bottom to top, the dashed grey line shows absorption efficiencies calculated with the DHS theory (with f max = 1) from the optical constant of Sogawa et al (2006) these differences, especially at about 10 μm, arise from a simplified treatment of the crystal anisotropy in the scattering theories. At this point, it is important to note that HD 69830 is not the only object for which these differences will be a problem.…”

“…2 provide a much better match. Consequently, we discarded the absorption efficiencies computed with the optical constant from Sogawa et al (2006), and used the aerosol measurements to represent crystalline olivine grains in our modelling. The great advantage of the aerosol technique is that it minimizes not only the contamination by environmental effects, but also eliminates possible computational artefacts inherited from the scattering theory.…”

“…5 where we show the Q abs values for Mg-and Fe-rich olivine 0.1 μm-sized grains (solid black and dashed red lines, respectively). To compute these Q abs values for different grain sizes, we first used the DHS theory (with f max = 1) for different grain sizes (between 0.1 and 1.0 μm) on the combination of both near-IR optical constant from Zeidler et al (2011) and Sogawa et al (2006) (at longer wavelengths). In the range 7 ≤ λ ≤ 40 μm (data from Zeidler et al 2011, stop at 7 μm), we then replaced the resulting absorption efficiencies with the aerosol measurements from Tamanai & Mutschke (2010), which are representative of grains smaller than 1 μm (the size distribution in the aerosol apparatus being unknown).…”

“…To account for this dirtiness, we used the Maxwell-Garnett effective medium theory to mix different fractions of carbon ("cel600", Jäger et al 1998b) with Mg-and Fe-rich crystalline olivine grains. The carbon admixture was performed on the combined optical constant from Zeidler et al (2011) and Sogawa et al (2006). We then replaced the resulting Q abs values with the normalized aerosol data for Mg-and Fe-rich olivine grains in the range 7 ≤ λ ≤ 40 μm (see last paragraph of Sect.…”

DUST PROPERTIES AND DISK STRUCTURE OF EVOLVED PROTOPLANETARY DISKS IN Cep OB2: GRAIN GROWTH, SETTLING, GAS AND DUST MASS, AND INSIDE-OUT EVOLUTION

“…Although the silicate emission at ∼10 μm and ∼20 μm traces only a small part of the dust content in the disk (small grains in the optically thin disk atmosphere with temperatures T ∼ 150-450 K; Calvet et al 1992;Natta et al 2000), the presence or absence of crystalline grains and the grain size can reveal information about heating processes in the disk, irradiation, transport, and turbulence (Meeus et The TLTD method (see J09 for details) reproduces the silicate feature using a multicomponent continuum, including emission from the stellar photosphere, an inner rim, and the optically thick disk midplane. It considers a collection of four different dust species with sizes 0.1, 1.5, and 6.0 μm: amorphous silicates with olivine and pyroxene stoichiometry (Dorschner et al 1995), forsterite (Sogawa et al 2006), amorphous silica (Henning & Mutschke 1997), and, in addition, enstatite grains (Jäger et al 1998) with sizes 0.1 and 1.5 μm (since the emission of 6 μm enstatite grains is indistinguishable from the continuum in cases of low S/N; see J09). The mass absorption coefficients are calculated from the material optical constants assuming that the crystalline grains can be assimilated to a Distribution of Hollow Spheres (Min et al 2005), and considering standard Mie theory for spherical particles for the amorphous dust.…”