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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. http://micro.magnet.fsu.edu/primer/java/polarizedlight/filters/index.html. http://lectureonline.cl.msu.edu/~mmp/kap24/polarizers/Polarizer.htm. http://ngsir.netfirms.com/englishhtm/Polarization.htm.

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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 http://micro.magnet.fsu.edu/primer/java/polarizedlight/filters/index.html http://lectureonline.cl.msu.edu/~mmp/kap24/polarizers/Polarizer.htm http://ngsir.netfirms.com/englishhtm/Polarization.htm

  3. Interstellar Polarization (Hiltner, Hall, etc.1948) Stars with d < 400 pc Stars with 2 < d < 4 kpc

  4. Linear Polarization Circular Polarization

  5. Polarization by Reflection perpendicular to plane of incidence parallel to plane of incidence Brewster’s angle

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

  7. oblate spheroid model (sphere) Polarization model 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?

  8. VUV optimized HD 204827 VIR optimized “compromise” HD 99872 Note: model fits with “astronomical silicates” seem to work better using oblate rather than prolate spheroids

  9. 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)

  10. Or is it????

  11. 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

  12. Polarization by Scattering

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

  14. GG Tau - circumstellar ring

  15. 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)

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

  17. Polarized Intensity Imaging Helps suppress unpolarized light coming directly from the star to reveal faint features

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