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Exploring Exoplanetary Atmospheric Scattering with Polarized Light

Detecting polarized light from exoplanetary atmospheres through polarimetry, revealing insights into orbital dynamics and atmospheric composition. Conducted observations with advanced equipment and analysis techniques. Results suggest the presence of small particles in the atmosphere.

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Exploring Exoplanetary Atmospheric Scattering with Polarized Light

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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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