Crystalline Silicate Feature of the Vega-like Star HD 145263

Honda, Mitsuhiko; Kataza, Hirokazu; Okamoto, Y.; Miyata, Takashi; Yamashita, Takuya; Sako, Shigeyuki; Fujiyoshi, Takuya; Ito, Meguru; Okada, Yoko; Sakon, Itsuki; Onaka, Takashi

doi:10.1086/423242

Cited by 42 publications

(56 citation statements)

References 37 publications

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“…In order to minimize the number of free parameters in the fitting procedure, we want to sample the size distribution carefully. We find that the variety of spectral shapes can be best covered using only two distinct particle sizes, a "small" particle size with a material volume equivalent sphere radius r V = 0.1 µm and a "large" particle size with r V = 1.5 µm (for a similar approach see Bouwman et al 2001;Honda et al 2004). We have extensively checked that the results of the analysis using three, four or five particle sizes with volume equivalent radii ranging up to 3.5 µm do not change significantly.…”

Section: Size Of the Dust Grainsmentioning

confidence: 91%

A 10 $\mathsf{\mu}$m spectroscopic survey of Herbig Ae star disks: Grain growth and crystallization

Boekel

Min²,

Waters

et al. 2005

A&A

278

402

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Abstract. We present spectroscopic observations of a large sample of Herbig Ae stars in the 10 µm spectral region. We perform compositional fits of the spectra based on properties of homogeneous as well as inhomogeneous spherical particles, and derive the mineralogy and typical grain sizes of the dust responsible for the 10 µm emission. Several trends are reported that can constrain theoretical models of dust processing in these systems: i) none of the sources consists of fully pristine dust comparable to that found in the interstellar medium; ii) all sources with a high fraction of crystalline silicates are dominated by large grains; iii) the disks around more massive stars (M > ∼ 2.5 M , L > ∼ 60 L ) have a higher fraction of crystalline silicates than those around lower mass stars, iv) in the subset of lower mass stars (M < ∼ 2.5 M ) there is no correlation between stellar parameters and the derived crystallinity of the dust. The correlation between the shape and strength of the 10 micron silicate feature reported by van Boekel et al. (2003) is reconfirmed with this larger sample. The evidence presented in this paper is combined with that of other studies to present a likely scenario of dust processing in Herbig Ae systems. We conclude that the present data favour a scenario in which the crystalline silicates are produced in the innermost regions of the disk, close to the star, and transported outward to the regions where they can be detected by means of 10 micron spectroscopy. Additionally, we conclude that the final crystallinity of these disks is reached very soon after active accretion has stopped.

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Section: Size Of the Dust Grainsmentioning

confidence: 91%

A 10 $\mathsf{\mu}$m spectroscopic survey of Herbig Ae star disks: Grain growth and crystallization

Boekel

Min²,

Waters

et al. 2005

A&A

278

402

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“…Telescope and sky emissions were removed by an additional nod throw of the same size, taken in the perpendicular direction for TIMMI2 and VISIR, and in the parallel direction to the chop for the MICHELLE observations. Honda et al(2004); j age from Zuckerman & Song (2004).…”

Section: Observationsmentioning

confidence: 99%

The nature of mid-infrared excesses from hot dust around Sun-like stars

Smith

Wyatt

Dent

2008

A&A

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Aims. Studies of the debris disk phenomenon have shown that most systems are analogous to the Edgeworth-Kuiper Belt (EKB). However a rare subset of sun-like stars possess dust which lies, in contrast, in the terrestrial planet region. In this study we aim to determine how many sources with apparent mid-infrared excess are truly hosts of warm dust, and investigate where the dust in these systems must lie. Methods. We observed using ground-based mid-infrared imaging with TIMMI2, VISIR and MICHELLE a sample of FGK main sequence stars previously reported to have hot dust. A new modelling approach was developed to determine the constraints that can be set on the radial extent of excess emission in such observations by demonstrating how the detectability of a disk of a given flux as a fraction of the total flux from the system (F disk /F total ) depends primarily on the ratio of disk radius to PSF width and on the uncertainty on that PSF width. Results. We confirm the presence of warm dust around three of the candidates; η Corvi, HD 145263 and HD 202406. For η Corvi modelling constrains the dust to lie in regions smaller than ∼3.5 AU. The modelling constrains the dust to regions smaller than 80−100 AU for HD 145263 and HD 202406, with SED fitting suggesting the dust lies at a few tens of AU. Of two alternative models for the η Corvi excess emission, we find that a model with one hot dust component at less than 0. 164 (<3 AU) (combined with the known submm dust population at ∼150 AU) fits all the data better at the 2.6σ level than an alternative model with two populations of dust emitting in the mid-infrared: hot dust at less than 0. 19 (<3.5 AU) and a mid-temperature component at ∼0. 66 (12 AU). We identify several systems which have a companion (HD 65277 and HD 79873) or background object (HD 53246, HD 123356 and HD 128400) responsible for their mid-infrared excess, and for three other systems we were able to rule out a point-like mid-infrared source near the star at the level of excess observed in lower resolution observations (HD 12039, HD 69830 and HD 191089). Conclusions. Hot dust sources are either young and possibly primordial or transitional in their emission, or have relatively small radius steady-state planetesimal belts, or they are old and luminous with transient emission. High resolution imaging can be used to constrain the location of the disk and help to discriminate between different models of disk emission. For some small disks, interferometry is needed to resolve the disk location.

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“…Bouwman et al 2001;Honda et al 2004;van Boekel et al 2004;van Boekel et al 2005) particle size effects have been modeled by using a typical size for the large particles of r V = 1.5 or 2.0 µm. The spectral signature of particles with these sizes is reported in these spectra.…”

Section: Homogeneous Spheres Porous Sphere Approximation Gaussian Ranmentioning

confidence: 99%

The 10 $\boldsymbol{\mu}$m amorphous silicate feature of fractal aggregates and compact particles with complex shapes

Min¹,

Dominik²,

Hovenier³

et al. 2006

A&A

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We model the 10 µm absorption spectra of nonspherical particles composed of amorphous silicate. We consider two classes of particles, compact ones and fractal aggregates composed of homogeneous spheres. For the compact particles we consider Gaussian random spheres with various degrees of non-sphericity. For the fractal aggregates we compute the absorption spectra for various fractal dimensions. The 10 µm spectra are computed for ensembles of these particles in random orientation using the well-known Discrete Dipole Approximation. We compare our results to spectra obtained when using volume equivalent homogeneous spheres and to those computed using a porous sphere approximation. We conclude that, in general, nonspherical particles show a spectral signature that is similar to that of homogeneous spheres with a smaller material volume. This effect is overestimated when approximating the particles by porous spheres with the same volume filling fraction. For aggregates with fractal dimensions typically predicted for cosmic dust, we show that the spectral signature characteristic of very small homogeneous spheres (with a volume equivalent radius r V 0.5 µm) can be detected even in very large particles. We conclude that particle sizes are underestimated when using homogeneous spheres to model the emission spectra of astronomical sources. In contrast, the particle sizes are severely overestimated when using equivalent porous spheres to fit observations of 10 µm silicate emission.Key words. infrared: general -stars: circumstellar matter -stars: planetary systems: protoplanetary disks IntroductionThe interpretation of absorption and emission spectra observed from astronomical objects requires knowledge of the absorption cross section as a function of the dust grain characteristics, such as size, shape and composition. Usually the absorption spectra are modeled using homogeneous spherical particles for which calculations can easily be done using Mie theory (Mie 1908). Although cosmic dust grains are in general not homogeneous spheres, in some cases Mie theory calculations can reproduce the observations quite accurately (see e.g. Hansen & Hovenier 1974;Kemper et al. 2004). However, in other cases one has to find a way of modeling the effects of particle shape in order to reproduce observations or laboratory measurements (see e.g. Mishchenko et al. 2000). It is therefore important to know the effects of the adopted particle shape model on the derived dust parameters, such as the particle size and structure (see e.g. Fabian et al. 2001;Min et al. 2003Min et al. , 2005a.From different formation mechanisms different types of particles may form. For example, when dust grains form from direct gas phase condensation, compact particles may be created. Alternatively, when dust grains stick together to form larger particles, complex aggregated structures may be formed. We study particles in both classes using irregularly shaped compact particles and fractal aggregates. For the compact particle shapes we use so-called Gaussian...

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Crystalline Silicate Feature of the Vega-like Star HD 145263

Cited by 42 publications

References 37 publications

A 10 $\mathsf{\mu}$m spectroscopic survey of Herbig Ae star disks: Grain growth and crystallization

A 10 $\mathsf{\mu}$m spectroscopic survey of Herbig Ae star disks: Grain growth and crystallization

The nature of mid-infrared excesses from hot dust around Sun-like stars

The 10 $\boldsymbol{\mu}$m amorphous silicate feature of fractal aggregates and compact particles with complex shapes

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