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 = days –R = R J –Inc =  Star K0V –M = 0.97 M sun –R = R sun –T eff = 5625 K –d = 300 pc

77 transits

 Latitude = o  Planetary & orbital parameters: –P p = d –P s = 4.54 d –a = A.U. (6.2 R * ) –i = o –R p = 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: 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.

0.665 I c 0.5 R p (R,I) 4 th transit

Spot lifetime: days Radius 1-Intensity

T eff =5625 K Intensity: I c Temperature: K Radius: R p

-85 o 125 o

Average spot number = 7

 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 = %

 “Planet radius” = R Jup (little larger than estimated without considering stellar spots) Radius R p ( )x10 4 km Intensity – temperature I c K Preferred longitudes-66 o, 114 o # spots – area coverage % 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)

32+11 days days