Radiative Alignment Of Dust Grains And Atoms: Tracing Magnetic Fields

Details Radiative Alignment Of Dust Grains And Atoms: Tracing Magnetic Fields Radiative Alignment Of Dust Grains And Atoms: Tracing Magnetic Fields

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...21113807h&link_type=abstract

American Astronomical Society, AAS Meeting #211, #138.07; Bulletin of the American Astronomical Society, Vol. 39, p.984

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Magnetic field plays crucial roles in many astrophysical processes (e.g., star formation, heat conduction and cosmic rays transport). One reliable way to study the topology of the magnetic field is based on polarized radiation of absorption and emission by aligned dust and atoms. We show that dust grains can be efficiently aligned by radiative torques (RATs) resulted from anisotropic radiation. Using an analytical model (AMO) for RATs, we show that grains tend to align with longer axes perpendicular to magnetic field, which corresponds to the Davis-Greenstein mechanism, but our model does not involve paramagnetic relaxation. We calculate the polarization arising from dust grains aligned with respect to a magnetic field, as a function of visual extinction for Taurus cloud, and obtain a good agreement with observation data.
The alignment of atoms provides a new technique to study magnetic fields. This technique is based on the ability of atoms with fine and hyperfine structure to be aligned in their ground or metastable state by anisotropic radiation. The alignment induces polarization of both scattered and absorbed radiation. As the aligned atoms precess in magnetic field, the field modifies the observed polarization. For instance, absorption lines get polarized with the polarization direction that reveals the direction of magnetic field. We show that the atomic alignment can provide unique information about the 3D magnetic field topology that is not available with any other technique. The expected degree of polarization may exceed 30\% for a favorable geometry of observations and therefore be easily detectable.

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