1. Nadiia Kostogryz & Svetlana Berdyugina
KIS science node:
Polarimetry
of Exoplanets
Nadiia Kostogryz & Svetlana Berdyugina

2. Outlines: Introduction to polarimetry of exoplanets
First detection of reflected polarized light from exoplanets
Confirmations of first detection
Other targets:  And b, 51 Peg b, WASP-4b
Polarimetry of transiting exoplanets
Advantage of polarimetric technique for grazing planets
Conclusions

3. Polarimetry of Exoplanets
Detection of reflected light  direct probe of planetary environment
Physics: scattering polarization
Polarization is perpendicular to the scattering plane
Max. polarization at 90 scattering angle
Stellar light is unpolarized (or modulated with a different period)
Polarization varies as planet orbits the star
polarimeter

4. HD189733
HD (Berdyugina et al. 2008)

5. First Detection: HD189733b B UB Transiting hot Jupiter
mass 1.15 MJ
period 2.2 d
semimajor axis 0.03 AU
B band (440nm, DiPol, KVA60)
(Berdyugina et al. 2008)
93 nightly measurements (3h), Stokes q & u
Individual errors ~(1-2)10–4
Error of binned data ~510–5
UBV (360,440,550nm, TurPol, NOT) (Berdyugina et al. 2011a)
35 nightly measurements(3-4h), Stokes q & u
29 standard stars for calibration: ~(1-2)10–5
Individual errors ~(2-4)10–5
Error of binned data ~110–5
Monte Carlo error analysis
Max amplitude 9x10–5  10–5
(Berdyugina et al. 2008) B
(Berdyugina et al. 2011a) UB

6. HD189733b: Blue Planet Geometrical Albedo: Strong function of 
0.61 at 400 nm,
0.28 at 550 nm,
<0.2 at 600 nm
<0.1 at >800 nm
Similar to that of Neptune
blue: Rayleigh and Raman scattering on H2
red: absorption by molecules
Conclusion:
HD is a Blue Planet

7. HD189733b: Blue Planet Secondary eclipse spectroscopy, HST
(Evans et al. 2013):
Geometrical albedo:

8. Transiting polarization
Chandrasekhar 1946: light scattered by free electrons or other scatterers emerges a partial linear polarization. The effect is a maximum at the limb, about 11% in the extreme case of a pure scattering atmosphere.
A linear polarization can occur if the star is not centrosymmetric.
Reasons for such anti-symmetry:
Eclipsing binary stars or
planet crosses the star;
A spot or spots appear on the star;
Kemp et al. 1983:
First detection of the Chandrasekhar effect in an eclipsing binary system Algol

9. Modeling of transiting polarization
Monte Carlo simulation of Chandrasekhar effect for
transiting planet
Carciofi & Magalhaes, 2005
Kostogryz et al., 2011a
Kostogryz, Yakobchuk & Vidmachenko 2011b
Frantseva, Kostogryz & Yakobchuk 2012
Monte Carlo simulation of Chandrasekhar effect for
transiting planet and spots
Inputs
Physical parameters of exoplanetary systems
exoplanets.eu
Center-to-limb polarization of the host star
(Fluri & Stenflo 1999, Stenflo 2005)
in progress
Limb darkening of the host star (Claret 2000)

10. HD189733 Transit (B-band) Spots and Transit (B-band)
Pmax ≈ 2.2 × 10-4 for HD189733
(Kostogryz et al. 2011a, 2011b)
Pmax ≈ 4.0 × 10-6 for HD189733
(Frantseva et al. 2012)
Spots and Transit (B-band)
Berdyugina et al., 2011 evaluated the p ≈ 3 × 10-6
Winn et al. (2007): starspots 1% Sstar; rotation period 13.4d

11. Corot-2 CoRoT-2: discovered in 2007 Spectral type: G7V (5575K)
M★ = 0.97MSun
R★ = 0.9 RSun
Rplanet = 1.465RJupiter
inclination = degree
P★ = 4.52 days
(Lanza et al. (2009))
Pplanet = 1.74 days.

12. Planet crosses the Solar type stars
HD209458: discovered in
1999
Spectral type: G0V (6075K)
Mstar/MSun = 1.148
Rstar/RSun = 1.146
Rplanet/RJupiter = 1.38
inclination = degree
Corot-1: discovered in 2007
Spectral type: G0V (6298K)
Mstar/MSun = 0.95
Rstar/RSun = 1.11
Rplanet/RJupiter = 1.49
inclination = 85.1 degree
TrES-2:
Spectral type: G0V (5850K)
Mstar/MSun = 0.98
Rstar/RSun = 1.0
Rplanet/RJupiter = 1.169
inclination = degree

13. Grazing planet crosses the star
Rpl/RJ = 1.169
inclination = 83.87°
Rpl/RJ = 1.169
inclination = 82.8°
Rpl/RJ = ×√2
inclination = 82.8°
Rpl/RJ = 1.169
inclination = 82.4°

14. Conclusions
Polarimetry is a differential technique with advantages for direct detection of exoplanets
composition of the atmosphere, weather pattern, rot. periods, magnetospheres, orbit orientation, etc
Polarimetry provides a detection tool for a much larger sample of exoplanets:
 non-transiting planets
 massive stars, binares
 evolved stars (giants)
 grazing planets
Different instruments provide consistent measurements
Rayleigh scattering with the strong wavelength dependence dominates the reflected light  blue planets
Polarimetry provides new physical insights into atmospheres (albedo, clouds)