Nadiia Kostogryz & Svetlana Berdyugina

KIS science node:

Polarimetry of

Exoplanets

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

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

pola

rim

ete

r

HD189733

HD189733 (Berdyugina et al. 2008)

First Detection: HD189733b• Transiting hot Jupiter

o mass 1.15 MJ

o period 2.2 do semimajor axis 0.03 AU

• B band (440nm, DiPol, KVA60)

(Berdyugina et al. 2008)

o 93 nightly measurements (3h), Stokes q & u

o Individual errors ~(1-2)10–4 o Error of binned data ~510–5

• UBV (360,440,550nm, TurPol, NOT) (Berdyugina et al. 2011a)

o 35 nightly measurements(3-4h), Stokes q & u

o 29 standard stars for calibration: ~(1-2)10–5

o Individual errors ~(2-4)10–5

o Error of binned data ~110–5

• Monte Carlo error analysis

• Max amplitude 9x10–5 10–5

(Berdyugina et al. 2011a)

(Berdyugina et al. 2008)

B

UB

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 Neptuneo blue: Rayleigh and Raman

scattering on H2

o red: absorption by molecules

Conclusion:HD189733 is a Blue Planet

HD189733b: Blue Planet• Secondary eclipse spectroscopy, HST

(Evans et al. 2013):

Geometrical albedo: 0.400.12 @300-450nm, <0.1 @450-590nm

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 orplanet 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

Modeling of transiting polarization

Carciofi & Magalhaes, 2005 Kostogryz et al., 2011a

Monte Carlo simulation of Chandrasekhar effect for transiting planet

Kostogryz, Yakobchuk & Vidmachenko 2011bFrantseva, 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)

HD189733Berdyugina et al., 2011 evaluated the p ≈ 3 × 10-6

Winn et al. (2007): starspots 1% Sstar; rotation period 13.4d

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)

Transit (B-band)

Corot-2

CoRoT-2: discovered in2007Spectral type: G7V (5575K)M★ = 0.97MSun

R★ = 0.9 RSun

Rplanet = 1.465RJupiter

inclination = 87.84 degreeP★ = 4.52 days(Lanza et al. (2009))Pplanet = 1.74 days.http://exoplanet.eu

Planet crosses the Solar type stars

HD209458: discovered in1999Spectral type: G0V (6075K)Mstar/MSun = 1.148Rstar/RSun = 1.146Rplanet/RJupiter = 1.38inclination = 86.59 degree

Corot-1: discovered in 2007Spectral type: G0V (6298K)Mstar/MSun = 0.95Rstar/RSun = 1.11Rplanet/RJupiter = 1.49inclination = 85.1 degree

TrES-2:Spectral type: G0V (5850K)Mstar/MSun = 0.98Rstar/RSun = 1.0Rplanet/RJupiter = 1.169inclination = 83.87 degree

Grazing planet crosses the star

Rpl/RJ = 1.169inclination = 83.87°

Rpl/RJ = 1.169inclination = 82.8°

Rpl/RJ = 1.169 ×√2inclination = 82.8°

Rpl/RJ = 1.169inclination = 82.4°

Conclusions• Polarimetry is a differential technique with advantages for

direct detection of exoplanetsÞ 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)