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5- Polarization Not for the faint of heart. Here there truly be dragons....

5- Polarization Not for the faint of heart. Here there truly be dragons. Preliminaries. Linear Polarization. Circular Polarization. Polarization by Reflection. Polarization by Extinction. (here tip toward/away from source - 90 deg is normal incidence). (sphere).

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5- Polarization Not for the faint of heart. Here there truly be dragons....

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  1. 5- Polarization Not for the faint of heart. Here there truly be dragons....

  2. Preliminaries

  3. Linear Polarization Circular Polarization

  4. Polarization by Reflection

  5. Polarization by Extinction (here tip toward/away from source - 90 deg is normal incidence)

  6. (sphere) Polarization profile (solid line) and extinction profile (dotted line) in the silicate band But 3.4 μm organic band is not polarized - can’t be coating silicates?

  7. HD 204827 HD 99872 Note: model fits with “astronomical silicates” seem to work better using oblate rather than prolate spheroids

  8. HD 161056 fit with Serkowski Law UV bump does not show up in polarization curve, so its carrier is not aligned Extinction curve of HD 161065 (circles) and ISM average (line)

  9. Or is it????

  10. Alignment Mechanisms • Magnetic Needles? - NO. Inconsistent with polarization maps • Paramagnetic Relaxation (Davis-Greenstein) - Induced B-field in kT-spinning grain lags alignment - dissipative torque aligns grain. Not efficient enough? • Superparamagnetic - like DG except uses ferromagnetic inclusions • Suprathermal Spin (Purcell) - rocket effect via H2 formation can achieve rotational energies greater than kT • Radiative Torques - anisotropic radiation field - overwhelmed by collisions • Streaming Flows (Gold) - requires unlikely organized gas flow perpendicular to galactic disk

  11. Polarization by Scattering

  12. Cep A Grayscale - radio continuum Thin rectangles - NIR pol

  13. GG Tau - circumstellar ring

  14. by way of introduction, let’s look at just intensity.. Henyey-Greenstein Scattering Phase Function (swiped from Dave Jewitt’s web page: http://www.ifa.hawaii.edu/~jewitt/beta.html Their H-G model used g=-0.5, i.e. backscattering)

  15. Example: AU Mic (Graham et al. 2007, ApJ 654, 595)

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