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| Paper: |
Spectropolarimetry of Interstellar Dust and Ice Features |
| Volume: |
449, Astronomical Polarimetry 2008: Science from Small to Large Telescopes |
| Page: |
93 |
| Authors: |
Whittet, D. C. B. |
| Abstract: |
The polarization counterparts to spectral features arising in solid particles are valuable diagnostics of grain physics, magnetic fields, and cloud structure in the interstellar medium. Useful constraints on grain models are placed by the occurrence (or non-occurrence) and strength of such counterparts. Of the various materials that produce observable absorption features, only those of silicates and ices show significant polarization; in contrast, features arising in carbonaceous dust typically lack any discernible polarized component. Observations of polarized silicate features enable the structure and mineralogy of interstellar and circumstellar silicates to be explored. The growth of ice mantles on silicate cores inside molecular clouds leads to new opportunities both to test grain alignment mechanisms and to map the magnetic fields within the clouds. Evidence for fractionation of grain materials arises in cases where rotation of the position angle of polarization across a feature is seen. The full potential of spectropolarimetry for such work has yet to be fully realized, however: to date, only a small sample of relatively bright sources has been studied. There is an urgent need for new observations of ice and silicate features in low-mass young stellar objects that represent good analogs of the early solar system, and in highly reddened field stars situated behind molecular clouds to provide spatial information on the distribution of polarization features in the icy molecular component of the clouds. These observations would be highly complementary to those of polarized emission from such regions at much longer infrared wavelength. |
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