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Florian Herzele SE Aktuelle Forschung zu Extrasolaren Planeten WS 07/08

First Detection of Polarized Scattered Light from an Exoplanetary Atmosphere Berdyugina et al. (12/2007). Florian Herzele SE Aktuelle Forschung zu Extrasolaren Planeten WS 07/08. Planetary Atmospheres.

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Florian Herzele SE Aktuelle Forschung zu Extrasolaren Planeten WS 07/08

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  1. First Detection of Polarized Scattered Light from an Exoplanetary AtmosphereBerdyugina et al. (12/2007) Florian Herzele SE Aktuelle Forschung zu Extrasolaren Planeten WS 07/08

  2. Planetary Atmospheres • Light scattered in planetary atmospheres is linearly polarized perpendicular to scattering plane • Characterized by Stokes parameters q and u, normalized to total flux • During revolution scattering angle changes = Stokes parameters vary •  Determination of orbital parameters

  3. System HD189733

  4. What they did and how • Observations in 2006-2007 with double image CCD polarimeter DIPol @ remotely controlled 60cm KVA telescope on La Palma • Rotating superachromatic plate as retarder and calcite plate as analyzer • Cylces of 16 exposures (retarder rotated at 22.5°)

  5. Stokes Parameter • X-axis: north-south Y-axis: east-west

  6. When they did it • 2006: 10-15s exposures @ 2x16 positions; =0.02-0.03% • 2007: 20-30s exposures @ 4x16 positions; =0.01-0.015% • Overall: 93 nightly measurements for each Stokes parameter

  7. Obtained Data

  8. Assumptions • Lambert sphere approximation • Rayleigh scattering • 2 minimization procedure • Simulated sample of Monte Carlo measurements

  9. Lambert Sphere • light falling on it is scattered such that the apparent brightness of the surface to an observer is the same regardless of the observer'sangle of view • Perfectly reflecting surface with geometrical albedo p=2/3

  10. Rayleigh Scattering

  11. 2 Distribution

  12. Orbital Parameters • Fixed paramters:orbital period P, transit / periastron epoch T0, semi-major axis a, radius of the star R* • Free parameters: eccentricity e, inclination i, longitude of the ascending node , radius of Lambert sphere RL, constant shift in Stokes parameters u and q

  13. Inclination • Inclination can be tested by photometric data but polarimetry can destinguish between i>90° (clockwise roation) and i<90° (counterclockwise) • At i=0° q and u have the same amplitude • For i≠0°: relative amplitude is influenced by , variations appear only at certain longitudes

  14. Best-fit Solution Errors of measurements have Gaussian distribution Signal is not spurious Solution is robust to errors

  15. Results 180° - ≈ < ≈30% if evaporating halo exists

  16. Interpretation • Excellent agreement between known values in e and i indicate plausibility of Rayleigh scattering • Planet has extended atmosphere effectively scattering in blue • Small particles like H, H2, H2O or even small dust grains (≤ 5m, e.g. silicate) might be present

  17. Planetary Motion

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