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Nadiia Kostogryz & Svetlana Berdyugina
KIS science node: Polarimetry of Exoplanets Nadiia Kostogryz & Svetlana Berdyugina
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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
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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
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HD189733 HD (Berdyugina et al. 2008)
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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 ~510–5 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 ~110–5 Monte Carlo error analysis Max amplitude 9x10–5 10–5 (Berdyugina et al. 2008) B (Berdyugina et al. 2011a) UB
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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
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HD189733b: Blue Planet Secondary eclipse spectroscopy, HST
(Evans et al. 2013): Geometrical albedo:
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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
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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)
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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
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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.
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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
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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°
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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)
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