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CoRoT-Exo-2 starspots physical characteristics

Adriana Silva-Válio (Mackenzie University – Brazil) A. F. Nucio (Osservatorio Astrofisico di Catania, Italy) R. Alonso and P. Barge (LAM - France). CoRoT-Exo-2 starspots physical characteristics. CoRoT Symp.: 02-05/02/2009. Starspots.

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CoRoT-Exo-2 starspots physical characteristics

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  1. Adriana Silva-Válio (Mackenzie University – Brazil) A. F. Nucio (Osservatorio Astrofisico di Catania, Italy) R. Alonso and P. Barge (LAM - France) CoRoT-Exo-2 starspots physical characteristics CoRoT Symp.: 02-05/02/2009

  2. Starspots • During one of its transits,an extra-solar planet may pass in front of a stellar group of spots creating a small variation in the stellar signal. • Light curve fitting by a model allows the study of the physical characteristics of starspots • Starspot model: Silva, ApJ Lett., 585, L147, 2003.

  3. Model • Star: modeled star with limb darkening • Planet: dark disc • Spot: modeled by three parameters: • Intensity, as a function of stellar intensity at disk center (max); • Size, as a function of planet radius; • Position, Latitude (restricted to transit path) and Longitude

  4. Transit Simulation • Planet opaque disk of radius r/Rs • Transit: every two minutes, the planet is centered at a given position in its orbit (aorb/Rsandi)  calculate the integrated flux by summing the intensity in all the pixels

  5. CoRoT-Exo-2 system • Planet • M sin(i) = 3.31 MJ • P = 1.7429964 days • R = 1.465 RJ • Inc = 87.84 • Star K0V • M = 0.97 Msun • R = 0.902 Rsun • Teff = 5625 K • d = 300 pc

  6. 77 transits

  7. Model 32nd transit 4th transit • Latitude = -14.6o • Planetary & orbital parameters: • Pp = 1.743 d • Ps = 4.54 d • a = 0.0288 A.U. (6.2 R*) • i = 87.84o • Rp = 0.172 R* Residuals Time (h)

  8. Spot model 77 transits (134 days) Stellar rotation=4.54 days Modeled 18 spots of fixed position: Latitude: -14.6o (transit line) Longitudes: -70 – +70o Models: a) Fit intensity with fixed radius (0.5 Rp) b) Fit radius with fixed intensity (0.3, 0.5, 0.665, 0.8 Icenter) c) Fit radius and intensity simultaneously.

  9. (R,I) 0.665 Ic 0.5 Rp 4th transit

  10. Spot temporal evolution Radius 1-Intensity Spot lifetime: 30 + 11 days

  11. Radius: 0.46+0.14 Rp Intensity: 0.60+0.13 Ic Temperature: 5010+240 K Teff=5625 K

  12. Preferred longitudes -85o 125o

  13. Spot number Average spot number = 7

  14. Area covered by spots Planet transit sweeps an area between latitudes -5o and -24o. Total area obscured by planet: Atot = 0.80 R*2 12% of solar hemisphere x1 2 Rp x2

  15. Spot area coverage Fitted spot radius and intensity: Area = 18.5 % Fitted only spot radius: Area = 10 - 40 %

  16. Spot mean characteristics “Planet radius” = 1.544 RJup (little larger than estimated without considering stellar spots)

  17. Future work Results expected: Starspot structure for Earth size planets; Stellar rotation (solar-like stars: 150 days ~ 5 periods) Extra: Differential rotation (spots at different latitudes); Activity cycles (for short cycles)

  18. Merci !

  19. Lifetime 32+11 days 29+11 days

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