Presentation on theme: "Adriana Silva-Válio (Mackenzie University – Brazil) A. F. Nucio (Osservatorio Astrofisico di Catania, Italy) R. Alonso and P. Barge (LAM - France) CoRoT."— Presentation transcript:
Adriana Silva-Válio (Mackenzie University – Brazil) A. F. Nucio (Osservatorio Astrofisico di Catania, Italy) R. Alonso and P. Barge (LAM - France) CoRoT Symp.: 02-05/02/2009
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.
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
Planet opaque disk of radius r/R s Transit: every two minutes, the planet is centered at a given position in its orbit (a orb /R s and i) calculate the integrated flux by summing the intensity in all the pixels
Planet –M sin(i) = 3.31 M J –P = 1.7429964 days –R = 1.465 R J –Inc = 87.84 Star K0V –M = 0.97 M sun –R = 0.902 R sun –T eff = 5625 K –d = 300 pc
Latitude = -14.6 o Planetary & orbital parameters: –P p = 1.743 d –P s = 4.54 d –a = 0.0288 A.U. (6.2 R * ) –i = 87.84 o –R p = 0.172 R * Time (h) Residuals 32 nd transit 4 th transit
77 transits (134 days) Stellar rotation=4.54 days Modeled 18 spots of fixed position: –Latitude: -14.6 o (transit line) –Longitudes: -70 – +70 o Models: –a) Fit intensity with fixed radius (0.5 R p ) –b) Fit radius with fixed intensity (0.3, 0.5, 0.665, 0.8 I center ) –c) Fit radius and intensity simultaneously.
Planet transit sweeps an area between latitudes -5 o and -24 o. Total area obscured by planet: –A tot = 0.80 R * 2 –12% of solar hemisphere 2 Rp x1x1 x2x2
Fitted spot radius and intensity: Area = 18.5 % Fitted only spot radius: Area = 10 - 40 %
“Planet radius” = 1.544 R Jup (little larger than estimated without considering stellar spots) Radius0.46+0.14 R p (5.0+1.5)x10 4 km Intensity – temperature0.60+0.13 I c 5010+240 K Preferred longitudes-66 o, 114 o # spots – area coverage7+17+118 - 20 % Lifetime31+11 daysno periodicity
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)