Modelling the optical properties of composite and porous interstellar grains

Вощинников, Н. В.; Ильин, В. П.; Henning, Th.

doi:10.1051/0004-6361:200400081

Cited by 96 publications

(118 citation statements)

References 47 publications

(63 reference statements)

Supporting

Mentioning

113

Contrasting

Order By: Relevance

“…Therefore fluffy structures with impurities and irregular grain shapes are more realistic. The cross section of composite particles (Krügel & Siebenmorgen 1994;Ossenkopf & Henning 1994;Voshchinnikov et al 2005), which are porous aggregates made up of silicate and carbon, vary when compared to homogeneous particles by a factor of 2 in the optical and by larger factors in the far IR/submm. We study the influence of the grain geometry on the cross section.…”

Section: Extinction Curvementioning

confidence: 99%

Dust in the diffuse interstellar medium

Siebenmorgen

Вощинников

Bagnulo

2014

A&A

Self Cite

109

123

View full text Add to dashboard Cite

We present a model for the diffuse interstellar dust that explains the observed wavelength-dependence of extinction, emission, and the linear and circular polarisation of light. The model is set up with a small number of parameters. It consists of a mixture of amorphous carbon and silicate grains with sizes from the molecular domain of 0.5 up to about 500 nm. Dust grains with radii larger than 6 nm are spheroids. Spheroidal dust particles have a factor 1.5-3 greater absorption cross section in the far-infrared than spherical grains of the same volume do. Mass estimates derived from submillimetre observations that ignore this effect are overestimated by the same amount. In the presence of a magnetic field, spheroids may be partly aligned and polarise light. We find that polarisation spectra help to determine the upper particle radius of the otherwise rather unconstrained dust size distribution. Stochastically heated small grains of graphite, silicates, and polycyclic aromatic hydrocarbons (PAHs) are included. We tabulate parameters for PAH emission bands in various environments. They show a trend with the hardness of the radiation field that can be explained by the ionisation state or hydrogenation coverage of the molecules. For each dust component its relative weight is specified so that absolute element abundances are not direct input parameters. The model is compared to the average properties of the Milky Way, which seem to represent dust in the solar neighbourhood. It is then applied to specific sight lines towards four particular stars, with one of them located in the reflection nebula NGC 2023. For these sight lines, we present ultra-high signal-to-noise linear and circular spectro-polarimetric observations obtained with FORS at the VLT. Using prolate rather than oblate grains gives a better fit to observed spectra; the axial ratio of the spheroids is typically two and aligned silicates are the dominant contributors to the polarisation.

show abstract

Section: Extinction Curvementioning

confidence: 99%

Dust in the diffuse interstellar medium

Siebenmorgen

Вощинников

Bagnulo

2014

A&A

Self Cite

109

123

View full text Add to dashboard Cite

show abstract

“…In principle, holes of different sizes can be assumed within a grain. Voshchinnikov et al (2005) adopted a size distribution of the holes in their model, in which the probability of the presence of a hole is assumed to be inversely proportional to its volume. The holes in our grain model are determined both by the number of dipoles and the process of the grain generation (Sect.…”

Section: Porous Grain Modelmentioning

confidence: 99%

“…Grain segregation (Roccatagliata et al 2009) or the occurrence of ice ) affect the value of the blowout size as well (Augereau et al 2001). However, another possible explanation for this problem can be the nature of the porous particles, which requires more investigations, since porosity influences the scattering and absorption properties of the particles (Voshchinnikov & Mathis 1999;Voshchinnikov et al 2005Voshchinnikov et al , 2006.…”

Section: β-Ratio and Blowout Sizementioning

confidence: 99%

Porous dust grains in debris disks

Kirchschlager

Wolf

2013

A&A

View full text Add to dashboard Cite

Aims. When modeling the density and grain size distribution in debris disks, the minimum particle size is often significantly larger than the corresponding blowout size. While the dust particles are usually modeled as compact, homogenous spheres, we instead investigate the impact of porosity. The optical properties of porous particles are determined, and the influences of porosity on the blowout size and dust temperatures investigated. Methods. Using the method of discrete dipole approximation, we calculate the scattering and absorption cross sections of porous particles and derive the blowout size and the behavior of the dust temperature. Results. We determine the efficiency factors of absorption and the radiation pressure for porous particles, and investigate the influence on the β-ratio. Blowout sizes are calculated for various stellar luminosities and porosities, and an approximation equation is derived to estimate the blowout size as a function of these parameters. Furthermore, we investigate the influence of the porosity on the dust equilibrium temperature. Conclusions. The blowout size increases with the particle porosity and stellar luminosity. The dust temperature of porous particles is lower than the one of the compact spheres; in particular, the temperature of blowout grains decreases for porous particles.

show abstract

“…According to Mie theory, astronomical silicate grains with a > 1 μm should have ω ≈ 0.55 from visible to nearinfrared wavelengths (Voshchinnikov et al 2005). We used this value in the LTE calculations intrinsic to our SED model.…”

Section: Modeling the Infrared Sedmentioning

confidence: 99%

HUBBLEANDSPITZER SPACE TELESCOPEOBSERVATIONS OF THE DEBRIS DISK AROUND THE NEARBY K DWARF HD 92945

Golimowski

Krist

Stapelfeldt

et al. 2011

The Astronomical Journal

View full text Add to dashboard Cite

We present the first resolved images of the debris disk around the nearby K dwarf HD 92945, obtained with the Hubble Space Telescope's (HST 's) Advanced Camera for Surveys. Our F606W (Broad V) and F814W (Broad I) coronagraphic images reveal an inclined, axisymmetric disk consisting of an inner ring about 2. 0-3. 0 (43-65 AU) from the star and an extended outer disk whose surface brightness declines slowly with increasing radius approximately 3. 0-5. 1 (65-110 AU) from the star. A precipitous drop in the surface brightness beyond 110 AU suggests that the outer disk is truncated at that distance. The radial surface-density profile is peaked at both the inner ring and the outer edge of the disk. The dust in the outer disk scatters neutrally but isotropically, and it has a low V-band albedo of 0.1. This combination of axisymmetry, ringed and extended morphology, and isotropic neutral scattering is unique among the 16 debris disks currently resolved in scattered light. We also present new infrared photometry and spectra of HD 92945 obtained with the Spitzer Space Telescope's Multiband Imaging Photometer and InfraRed Spectrograph. These data reveal no infrared excess from the disk shortward of 30 μm and constrain the width of the 70 μm source to 180 AU. Assuming that the dust comprises compact grains of astronomical silicate with a surface-density profile described by our scattered-light model of the disk, we successfully model the 24-350 μm emission with a minimum grain size of a min = 4.5 μm and a size distribution proportional to a −3.7 throughout the disk, but with maximum grain sizes of 900 μm in the inner ring and 50 μm in the outer disk. Together, our HST and Spitzer observations indicate a total dust mass of ∼0.001M ⊕ . However, our observations provide contradictory evidence of the dust's physical characteristics: its neutral V-I color and lack of 24 μm emission imply grains larger than a few microns, but its isotropic scattering and low albedo suggest a large population of submicron-sized grains. If grains smaller than a few microns are absent, then stellar radiation pressure may be the cause only if the dust is composed of highly absorptive materials like graphite. The dynamical causes of the sharply edged inner ring and outer disk are unclear, but recent models of dust creation and transport in the presence of migrating planets support the notion that the disk indicates an advanced state of planet formation around HD 92945.

show abstract

Modelling the optical properties of composite and porous interstellar grains

Cited by 96 publications

References 47 publications

Dust in the diffuse interstellar medium

Dust in the diffuse interstellar medium

Porous dust grains in debris disks

HUBBLEANDSPITZER SPACE TELESCOPEOBSERVATIONS OF THE DEBRIS DISK AROUND THE NEARBY K DWARF HD 92945

Contact Info

Product

Resources

About