Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...209.1718y&link_type=abstract
2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #17.18; Bulletin of the American Astronomical Society, V
Astronomy and Astrophysics
Astronomy
Scientific paper
Atoms and ions with fine and hyperfine structure of levels can be aligned in their ground or metastable state by external radiation. The alignment here is understood in terms of projection of atomic angular momentum, if a classical picture is used. The atomic alignment induces the polarization of absorption lines and modification of the emission lines. As the species precess in magnetic field the field modifies the polarization. We show that the topology of fields weaker than one Gauss can be studied by polarimetry. In addition, depending on the distance from a pumping source and magnetic field strength, there could be different regimes that provide additional information on magnetic fields. For instance, magnetic splitting, when it is comparable to the line-width, changes the atomic occupations and coherence on their excited state, and thus changes the polarization pattern of resonant-scattered light. This is known as Hanle effect. We discuss how this effect is modified in the presence of atomic alignment.
We also report a ground state Hanle effect, which takes place when the precession rate becomes comparable with the pumping rate of the source. We provide predictions of the atomic line polarizations in various regimes and for a variety of atomic species and outline the exciting prospects of the technique for studies of magnetic fields within circumstellar regions, interplanetary medium, interstellar medium and AGNs.
Lazarian Alex
Yan Huirong
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