Collisional charging of interstellar grains

Draine, B. T.; Sutin, Brian M.

doi:10.1086/165596

Cited by 419 publications

(526 citation statements)

References 2 publications

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“…6). Above this transition, the charge residing on grains is unimportant in determining the abundances of ions and electrons and their occasional sticking onto grains yields a mean charge Z g (a) e ≈ −4kT a/e on grains of radius a (Spitzer 1941;Draine & Sutin 1987). The total charge per unit volume carried by grains with a size distribution x g (a) (where the number density of grains with radii between a and a + da is n H x g (a) da) is therefore x g (a)Z g (a) da.…”

Section: Discussionmentioning

confidence: 99%

“…The simple chemical reaction scheme of Nishi, Nakano & Umebayashi (1991) and Sano et al (2000) is adopted, which follows the abundances of the light ions H + , H + 3 , He + , C + , and representative heavier molecular and metal ions (denoted m + and M + respectively), as well as charged grains. Their scheme has been extended to include high grain charge using the cross sections of Draine & Sutin (1987). This is necessary because the temperatures here are high compared to molecular clouds -the high thermal velocities of electrons can overcome large Coulomb barriers allowing grains to pick up a high charge through electron sticking.…”

Section: Diffusivity Calculationsmentioning

confidence: 99%

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Magnetic fields in protoplanetary disks

Wardle

2007

Astrophys Space Sci

255

341

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Magnetic fields likely play a key role in the dynamics and evolution of protoplanetary disks. They have the potential to efficiently transport angular momentum by MHD turbulence or via the magnetocentrifugal acceleration of outflows from the disk surface. Magnetically-driven mixing has implications for disk chemistry and evolution of the grain population, and the effective viscous response of the disk determines whether planets migrate inwards or outwards. However, the weak ionisation of protoplanetary disks means that magnetic fields may not be able to effectively couple to the matter. I examine the magnetic diffusivity in a minimum solar nebula model and present calculations of the ionisation equilibrium and magnetic diffusivity as a function of height from the disk midplane at radii of 1 and 5 AU. Dust grains tend to suppress magnetic coupling by soaking up electrons and ions from the gas phase and reducing the conductivity of the gas by many orders of magnitude. However, once grains have grown to a few microns in size their effect starts to wane and magnetic fields can begin to couple to the gas even at the disk midplane. Because ions are generally decoupled from the magnetic field by neutral collisions while electrons are not, the Hall effect tends to dominate the diffusion of the magnetic field when it is able to partially couple to the gas, except at the disk surfaces where the low density of neutrals permits the ions to remain attached to the field lines.For a standard population of 0.1µm grains the active surface layers have a combined column Σ active ≈ 2 g cm −2 at 1 AU; by the time grains have aggregated to 3 µm, Σ active ≈ 80 g cm −2 . Ionisation in the active layers is dominated by stellar x-rays. In the absence of grains, x-rays maintain magnetic coupling to 10% of

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Section: Discussionmentioning

confidence: 99%

Section: Diffusivity Calculationsmentioning

confidence: 99%

Magnetic fields in protoplanetary disks

Wardle

2007

Astrophys Space Sci

255

341

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“…Photoelectric grain currents are found using Draine (1978) using the dust absorption data from Laor & Draine (1993). Collisions with electrons and protons are considered assuming the standard "" sticking ÏÏ coefficients, following Draine (1978) and Draine & Sutin (1987). More details of the dust physics in MAPPINGS III can be found in .…”

Section: Starburst Modelingmentioning

confidence: 99%

Theoretical Modeling of Starburst Galaxies

Kewley

Dopita

Sutherland

et al. 2001

ApJ

2,539

110

3,967

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We have modeled a large sample of infrared starburst galaxies using both the PEGASE v2.0 and STARBURST99 codes to generate the spectral energy distribution (SED) of the young star clusters. PEGASE utilizes the Padova group tracks, while STARBURST99 uses the Geneva group tracks, allowing comparison between the two. We used our MAPPINGS III code to compute photoionization models that include a self-consistent treatment of dust physics and chemical depletion. We use the standard optical diagnostic diagrams as indicators of the hardness of the EUV radiation Ðeld in these galaxies. These diagnostic diagrams are most sensitive to the spectral index of the ionizing radiation Ðeld in the 1È4 ryd region. We Ðnd that warm infrared starburst galaxies contain a relatively hard EUV Ðeld in this region. The PEGASE ionizing stellar continuum is harder in the 1È4 ryd range than that of STARBURST99. As the spectrum in this regime is dominated by emission from Wolf-Rayet (W-R) stars, this discrepancy is most likely due to the di †erences in stellar atmosphere models used for the W-R stars. The PEGASE models use the Clegg & Middlemass planetary nebula nuclei (PNN) atmosphere models for the W-R stars, whereas the STARBURST99 models use the Schmutz, Leitherer, & Gruenwald W-R atmosphere models. We believe that the Schmutz et al. atmospheres are more applicable to the starburst galaxies in our sample ; however, they do not produce the hard EUV Ðeld in the 1È4 ryd region required by our observations. The inclusion of continuum metal blanketing in the models may be one solution. Supernova remnant (SNR) shock modeling shows that the contribution by mechanical energy from SNRs to the photoionization models is >20%. The models presented here are used to derive a new theoretical classiÐcation scheme for starbursts and active galactic nucleus (AGN) galaxies based on the optical diagnostic diagrams.

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“…For each run, we select M, α, φ by initially selecting a representative temperature T for cold, molecular gas and box size Lbox, then estimating the Mach number and mean density corresponding to observed GMCs on the linewidth-size and mass-size relations from Bolatto et al (2008). We then populate the box with four (relatively large) 5 physical grain sizes (α), and determine the charge Z d (and φ) of each following Draine & Sutin (1987) 6 : Z d = −1/(1+0.037 τ −1/2 )−2.5 τ where τ ≡ a d k T /e 2 . For comparison, we consider some cases with Z d = 0 (no Lorentz forces; our "noZ" runs) or 10× larger charge (our "hiZ" runs) -this crudely corresponds to the expected values if the gas were 10× hotter (but retained the same Mach number).…”

Section: [Dex]mentioning

confidence: 99%

“…5 We focus on large grains a d ∼ 0.1 − 10 µm because (1) these contain most of the dust mass, and (2) smaller grains are tightly-coupled to the gas and therefore exhibit less extreme dust-to-gas fluctuations. 6 Draine & Sutin (1987) estimate grain charges based on a pure collisional model for large grains and a polarization model for small grains. Shull (1978) show that accounting for higher-order effects can lower the charge by a factor ∼ 2 when the dust-gas motion is highly supersonic.…”

Section: Dust Magnetizationmentioning

confidence: 99%

The dynamics of charged dust in magnetized molecular clouds

Lee

Hopkins

Squire

2017

Monthly Notices of the Royal Astronomical Society

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We study the dynamics of large, charged dust grains in turbulent giant molecular clouds (GMCs). Massive dust grains behave as aerodynamic particles in primarily neutral dense gas, and thus are able to produce dramatic small-scale fluctuations in the dust-to-gas ratio. Hopkins & Lee (2016) directly simulated the dynamics of neutral dust grains in super-sonic MHD turbulence, typical of GMCs, and showed that the dust-to-gas fluctuations can exceed factor ∼ 1000 on small scales, with important implications for star formation, stellar abundances, and dust behavior and growth. However, even in primarily neutral gas in GMCs, dust grains are negatively charged and Lorentz forces are non-negligible. Therefore, we extend our previous study by including the effects of Lorentz forces on charged grains (in addition to drag). For small charged grains (sizes 0.1 µm), Lorentz forces suppress dust-to-gas ratio fluctuations, while for large grains (sizes 1 µm), Lorentz forces have essentially no effect, trends that are well explained with a simple theory of dust magnetization. In some special intermediate cases, Lorentz forces can enhance dust-gas segregation. Regardless, for the physically expected scaling of dust charge with grain size, we find the most important effects depend on grain size (via the drag equation) with Lorentz forces/charge as a second-order correction. We show that the dynamics we consider are determined by three dimensionless numbers in the limit of weak background magnetic fields: the turbulent Mach number, a dust drag parameter (proportional to grain size) and a dust Lorentz parameter (proportional to grain charge); these allow us to generalize our simulations to a wide range of conditions.

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Collisional charging of interstellar grains

Cited by 419 publications

References 2 publications

Magnetic fields in protoplanetary disks

Magnetic fields in protoplanetary disks

Theoretical Modeling of Starburst Galaxies

The dynamics of charged dust in magnetized molecular clouds

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