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Astronomical Polarimetry

I have been involved in the development of a number of polarimetry systems for the AAT and other telescopes, working in collaboration with the group at the University of Hertfordshire. These systems include a spectropolarimetry system for the RGO spectrograph on the AAT, and an imaging polarimetry system using TAURUS on the AAT. We have recently built a high sensitivity polarimeter, PlanetPol, capable of measuring stellar polarization to one part in a million.

These and other earlier instruments have been used for a range of research projects including the following:

  • A study of polarization in young stellar objects has led to the discovery of suprisingly high levels of IR circular polarization in regions of massive star formation such as Orion OMC-1. The circular polarization is interpreted as being due to scattering from aligned aspherical dust grains. We have suggested that circular polarization produced in this way may be a possible explanation for the origin of biomolecular homochirality (see: Chirality and the Origin of Life).
  • Spectropolarimetric studies of a sample of Seyfert 2 galaxies have been used to study the incidence of "hidden broad line regions" visible in polarized flux. It is found that the Seyferts with hidden broad line regions have warmer far-infrared colours than those without hidden broad line regions. These results can be explained as a consequence of different inclinations in terms of the unified model of Seyfert galaxies.
  • Studies of polarization in magnetic cataclysmic variables (AM Her binaries or Polars) have been used as a way of studying the structure and evolution of these systems. The polarization arises from the process of cyclotron radiation in material accreting onto the magnetic white dwarf. This radiation can be highly circularly polarized, and can in some cases show discrete cyclotron harmonics in the spectrum which can be used to determine the magnetic field of the white dwarf.



See also:  Chirality and the Origin of Life

Alexander, D.M., Heisler, C.A., Young, S., Bailey, J., Hough, J.H., Lumsden, S.L., 2000, Constraints on the nuclear emission of the Circinus galaxy: optical and near-IR spectropolarimetry, Mon. Not. R. Astron. Soc. 313, 815. (ADS)

Young, S., Corbett, E.A., Gianuzzo, M.E., Hough, J.H., Robinson, A., Bailey, J. and Axon, D.J. 1999, A time-variable scattered component to broad H-alpha in the Seyfert 1 galaxy Mrk 509, Mon. Not. R. Astron. Soc. 303, 227. (ADS)

Alexander, D.M., Hough, J.H., Young, S., Bailey, J.A., Heisler, C.A., Lumsden, S.L. and Robinson, A., 1999, Searching for the hidden broad-line region in Centaurus A, Mon. Not. R. Astron. Soc. 303, L17. (ADS)

Buckley, D.A.H., Ferrario, L., Wickramasinghe, D.T. and Bailey, J., 1998, Polarimetry of the eclipsing polar RX J0929.1-2404, Mon. Not. R. Astron. Soc. 295, 899. (ADS)

Packham, C., Young, S., Hough, J.H., Axon, D.J. and Bailey, J., 1997, Near-infrared imaging polarimetry of NGC 1068, Mon. Not. R. Astron. Soc. 288, 375. (ADS)

Heisler, C.A., Lumsden, S.L. and Bailey, J. 1997, Visibility of scattered broad-line emission in Seyfert 2 galaxies, Nature, 385, 700. (ADS)