nadiia kostogryz & svetlana berdyugina kis science node: polarimetry of exoplanets
TRANSCRIPT
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)