Dust amorphization in protoplanetary disks

Glauser, Adrian M.; Güdel, M.; Watson, D. M.; Henning, Th.; Schegerer, Alexander; Wolf, S.; Audard, M.; Baldovin-Saavedra, C.

doi:10.1051/0004-6361/200912087

Cited by 23 publications

(25 citation statements)

References 47 publications

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“…Above this luminosity value no trend is visible. Still, we observe that objects with high X-ray luminosities seem to have higher crystalline fractions, which seems at first in contradiction with the conclusion by Glauser et al (2009). Given the limited number of objects for which we have X-ray data in our sample, however, we were not able to perform any age selection as in Glauser et al (2009).…”

Section: Silicate Crystallization and Amorphizationcontrasting

confidence: 85%

“…This study shows that, obviously, the accretion activity may have a strong impact on the dust chemistry in circumstellar disks. Recently, Glauser et al (2009) identified an anti-correlation between X-ray luminosity of the stars and crystalline fraction for the warm disk component (C warm in Sect. 3.2).…”

Section: Silicate Crystallization and Amorphizationmentioning

confidence: 99%

“…In a similar approach as Glauser et al (2009), we attempt to investigate the impact of high-energy particles, assumed to be traced by X-ray luminosity, on the disk mineralogy. Table 2 displays the X-ray luminosities (in units of erg s −1 ) available in the literature or obtained by fitting the spectra from the Second XMM-Newton serendipitous source catalogue (Watson et al 2009b) with the X-ray emission from one or two-temperature plasma combined with photoelectric absorption, for a subset of 17 objects among our stellar sample analyzed with the B2C compositional fitting model.…”

Section: Silicate Crystallization and Amorphizationmentioning

confidence: 99%

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C2D Spitzer-IRS spectra of disks around T Tauri stars

Olofsson¹,

Augereau²,

Dishoeck

et al. 2010

A&A

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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.

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Section: Silicate Crystallization and Amorphizationcontrasting

confidence: 85%

Section: Silicate Crystallization and Amorphizationmentioning

confidence: 99%

Section: Silicate Crystallization and Amorphizationmentioning

confidence: 99%

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C2D Spitzer-IRS spectra of disks around T Tauri stars

Olofsson¹,

Augereau²,

Dishoeck

et al. 2010

A&A

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“…Once again, we run the Kendall τ test, and find essentially no significant correlation in the warm disk regions (τ = −0.27, p = 0.10) and the colder parts of the disks (τ = −0.02, p = 0.88). Glauser et al (2009) suggested that irradiation of dust grains by energetic ions from the stellar winds of young stars can amorphize the surface layer of the protoplanetary dust very efficiently, thus erasing any correlation between crystalline mass fraction and stellar parameters, such as bolometric luminosity, effective temperature, accretion rate, or disk geometry. Ábrahám et al (2009) discovered that episodes of increased accretion may create new crystals.…”

Section: (B) Dust Properties Of Disks Around Cool T Tauri Starsmentioning

confidence: 99%

Young stars inϵChamaleontis and their disks: disk evolution in sparse associations

Fang

Boekel

Bouwman

et al. 2012

A&A

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Context. The nearby young stellar association Cha has an estimated age of 3-5 Myr, making it an ideal laboratory to study the disk dissipation process and provide empirical constraints on the timescale of planet formation. Aims. We wish to complement existing optical and near-infrared data of the Cha association, which provide the stellar properties of its members, with mid-infrared data that probe the presence, geometry, and mineralogical composition of protoplanetary disks around individual stars. Methods. We combine the available literature data with our Spitzer/IRS spectroscopy and VLT/VISIR imaging data. We use proper motions to refine the membership of Cha. Masses and ages of individual stars are estimated by fitting model atmospheres to the optical and near-infrared photometry, followed by placement in the Hertzsprung-Russell diagram. The Spitzer/IRS spectra are analyzed using the two-layer temperature distribution spectral decomposition method. Results. Two stars previously identified as members, CXOU J120152.8 and 2MASS J12074597, have proper motions that are very different from those of the other stars. But other observations suggest that the two stars are still young and thus might still be related to Cha. HD 104237C is the lowest mass member of Cha with an estimated mass of ∼13-15 Jupiter masses. The very low mass stars USNO-B120144.7 and 2MASS J12005517 show globally depleted spectral energy distributions, pointing at strong dust settling. 2MASS J12014343 may have a disk with a very specific inclination, where the central star is effectively screened by the cold outer parts of a flared disk, but the 10 μm radiation of the warm inner disk can still reach us. We find that the disks in sparse stellar associations are dissipated more slowly than those in denser (cluster) environments. We detect C 2 H 2 rovibrational band around 13.7 μm on the IRS spectrum of USNO-B120144.7. We find strong signatures of grain growth and crystallization in all Cha members with 10 μm features detected in their IRS spectra. We combine the dust properties derived in the Cha sample with those found using identical or similar methods in the MBM 12, Coronet, η Cha associations, and in the cores-to-disks legacy program. We find that disks around low-mass young stars show a negative radial gradient in the mass-averaged grain size and mass fraction of crystalline silicates. A positive correlation exists between the mass-averaged grain sizes of amorphous silicates and the accretion rates if the latter is above ∼10 −9 M yr −1 , possibly indicating that those disks are sufficiently turbulent to prevent grains of several microns in size to sink into the disk interior.

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“…Dolginov & Stepinski (1993) argue that the magnetic field will diffuse the cosmic rays paths through the atmosphere and, hence, decrease the critical column density (or scale height) λ CR for cosmic ray attenuation. Glauser et al (2009) demonstrate that fast protons and He ions interact with dust grains in disks, hence, the dust will decrease the effective attenuation length in the atmosphere further. This suggests that a smaller fraction of the atmosphere and of the cloud is influenced by cosmic rays.…”

Section: Cosmic Ray Attenuationmentioning

confidence: 93%

Dust cloud lightning in extraterrestrial atmospheres

Helling

Jardine

Diver

et al. 2013

Planetary and Space Science

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Lightning is present in all solar system planets which form clouds in their atmospheres. Cloud formation outside our solar system is possible in objects with much higher temperatures than on Earth or on Jupiter: Brown dwarfs and giant extrasolar gas planets form clouds made of mixed materials and a large spectrum of grain sizes. These clouds are globally neutral obeying dustgas charge equilibrium which is, on short timescales, inconsistent with the observation of stochastic ionization events of the solar system planets. We argue that a significant volume of the clouds in brown dwarfs and extrasolar planets is susceptible to local discharge events and that the upper cloud layers are most suitable for powerful lightning-like discharge events. We discuss various sources of atmospheric ionisation, including thermal ionisation and a first estimate of ionisation by cosmic rays, and argue that we should expect thunderstorms also in the atmospheres of brown dwarfs and giant gas planets which contain mineral clouds.

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Dust amorphization in protoplanetary disks

Cited by 23 publications

References 47 publications

C2D Spitzer-IRS spectra of disks around T Tauri stars

C2D Spitzer-IRS spectra of disks around T Tauri stars

Young stars inϵChamaleontis and their disks: disk evolution in sparse associations

Dust cloud lightning in extraterrestrial atmospheres

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