Grain Alignment by Ambipolar Diffusion in Molecular Clouds

Roberge, W. G.; Hanany, Shaul; Messinger, David W.

doi:10.1086/176383

Cited by 60 publications

(76 citation statements)

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“…In outer parts of the coma and in the tail, the alignment via radiative torques and interaction with solar wind could be important. For the comet environment the most important are mechanical alignment of grains rotating thermally (Gold, 1952;Purcell, 1979;Dolginov and Mytrophanov, 1976;Lazarian, 1994Lazarian, , 1997aLazarian, ,1997bRoberge et al, 1995) and suprathermally (Lazarian, 1995;Lazarian et al, 1996;Lazarian and Draine, 1997;Lazarian and Efroimsky, 1999) and radiative torque alignment (Dolginov, 1972;Dolginov and Mytrophanov, 1976;Weingartner, 1996, 1997;Weingartner and Draine, 2003;Abbas et al, 2004;Cho and Lazarian, 2005). For the review of the mechanisms of grain alignment see Lazarian ( 2003).…”

Section: Scattering By Aligned Non-spherical Particlesmentioning

confidence: 99%

Circular polarization in comets: Observations of Comet C/1999 S4 (LINEAR) and tentative interpretation

Rosenbush

Kolokolova

Lazarian

et al. 2007

Icarus

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Comet C/1999 S4 (LINEAR) was exceptional in many respects. Its nucleus underwent multiple fragmentations culminating in the complete disruption around July 20, 2000. We present circular polarization measurements along the cuts through the coma and nucleus of the comet during three separate observing runs, in June 28-July 2, July 8-9, and July 21-22, 2000. The circular polarization was detected at a rather high level, up to 0.8%. The left-handed as well as right-handed polarization was observed over the coma with the left circularly polarized light systematically observed in the sunward part of the coma. During our observations the phase angle of the comet varied from 61 up to 122°, which allowed us to reveal variations of circular polarization with the phase angle. Correlation between the degree of circular polarization, visual magnitude, water production rate, and linear polarization of comet C/1999 S4 (LINEAR) during its final fragmentation in July 2000 was found.The mechanisms that may produce circular polarization in comets and specifically in comet C/1999 S4 (LINEAR) are discussed and some tentative interpretation is presented.

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Section: Scattering By Aligned Non-spherical Particlesmentioning

confidence: 99%

Circular polarization in comets: Observations of Comet C/1999 S4 (LINEAR) and tentative interpretation

Rosenbush

Kolokolova

Lazarian

et al. 2007

Icarus

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“…The ion-neutral velocity v ni was taken from a model of MHD disturbances in dense clouds developed by Roberge and co-workers (Roberge & Hanany 1990;Roberge et al 1995) and which was kindly made available to us. These numerical values of v ni are presented in terms of the dissipation time of Alfvén waves due to ion-neutral damping, τ ni .…”

Section: Ambipolar Diffusionmentioning

confidence: 99%

Deuterium fractionation along the TMC-1 ridge

Markwick¹,

Charnley²,

Millar³

2001

A&A

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Abstract. In this paper, we present a model to predict and explain the observed gradients in deuterium fractionation and molecular abundance along the TMC-1 ridge. In TMC-1, gradients in the level of deuterium fractionation are observed for all the molecular species for which the measurement has been made; HCO + , HC3N, C3H2 and HNC. The model is based on the assumption that the chemical evolution of the TMC-1 ridge has been affected by Alfvén waves. The structure of the model and its comparison with observations are discussed. We find that the model qualitatively and somewhat quantitatively reproduces the observations of the aforementioned molecular species. We present predictions of the fractionation gradients along the TMC-1 ridge for other molecules of observational interest.

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“…Almost any magnetic alignment mechanism leads to the alignment of the rotational axes of dust grains with the magnetic field, whether the mechanism operates by direct magnetic torquing of the dust grains (the classical Davis-Greenstein mechanism, and its many modern variations; e.g., Hildebrand 1988;Roberge 1996;Lazarian 1996) or via an intermediary such as streaming ions set in motion by moving magnetic field lines (Lazarian 1994;Roberge et al 1995). As a result, the mean projection of the long axis of the grains, and thus the dominant E-vector of thermal grain emission, is expected to be perpendicular to the magnetic field lines.…”

Section: Polarization Of Thermal Far-infrared and Suhmillimeter Contimentioning

confidence: 99%

“…A recent alternative was offered by Rosner and Bodo (1996), who propose that the relativistic electrons illuminating the NTF's are produced in the termination shocks of stellar winds, and that this process defines the transverse dimensions of the NTF's. In general, each filament would require a separate stellar wind, and the presence of bundles of NTF's would be ascribable to clusters of windy stars.…”

Section: Origin Of the Nonthermal Filamentsmentioning

confidence: 99%

“…Differential rotation winds and amplifies the perpendicular component, which now dominates the Galactic disk, and various dynamo mechanisms can provide further amplification (e.g., Ruzmaikin et al 1988). Its strength saturates as the rate of amplification is balanced by the rate of loss due to ambipolar diffusion out of the Galactic gas layer.…”

Section: · Origin Of the Central Dipole Fieldmentioning

confidence: 99%

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8.1. Magnetic phenomena in galactic nuclei

Morris

1998

Symp. - Int. Astron. Union

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Abstract. The magnetic environment of the Galactic nucleus contrasts sharply with that of the Galactic disk. The inner few hundred parsecs of our Galaxy appear to be dominated by a strong (~milligauss) and uniform dipole field which dominates the pressure within the central intercloud medium. An attractive hypothesis for the origin of the central vertical field is that it results from the concentration of protogalactic field by radial inflow of gas throughout the Galaxy's lifetime. The predominant orientation of the magnetic field within dense molecular clouds is parallel to the galactic plane, which can be understood in terms of the strong tidal shear to which these clouds are subjected . The contrasting geometries of the cloud and intercloud fields allow for magnetic field line reconnection at cloud surfaces, which, under the right circumstances, could produce the relativistic electrons which delineate the nonthermal radio filaments near the Galactic center with their synchrotron emission. The characteristics of the Galactic center "magnetosphere" should be generalizable to all gas-rich spiral galaxies. Inadequate spatial resolution currently prevents us from exploring magnetic fields in other galactic nuclei to the same depth as in the Galactic center, but existing evidence is consistent with similar magnetic geometries elsewhere.

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Grain Alignment by Ambipolar Diffusion in Molecular Clouds

Cited by 60 publications

References 0 publications

Circular polarization in comets: Observations of Comet C/1999 S4 (LINEAR) and tentative interpretation

Circular polarization in comets: Observations of Comet C/1999 S4 (LINEAR) and tentative interpretation

Deuterium fractionation along the TMC-1 ridge

8.1. Magnetic phenomena in galactic nuclei

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