1. 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

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 NameHD 189733 b Discovered in2005 M.sin i1.15 (± 0.046) MJ Semi major axis0.0312 (± 0.0004) AU Orbital period2.2185733 (± 2e-05) days Eccentricity0 Radius1.156 (± 0.032) RJ T transit 2453988.80336 (± 0.00024) Inclination85.76 (± 0.29) deg. Update18/04/07

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's angle 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 T 0, semi-major axis a, radius of the star R * Free parameters: eccentricity e, inclination i, longitude of the ascending node , radius of Lambert sphere R L, 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 (1)Errors of measurements have Gaussian distribution (2)Signal is not spurious (3)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, H 2, H 2 O or even small dust grains (≤ 5  m, e.g. silicate) might be present

17. Planetary Motion