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

CoRoT-Exo-2 starspots physical characteristics

StarspotsStarspots

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.

ModelModelStar: modeled star with

limb darkeningPlanet: dark discSpot: 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

Transit SimulationTransit Simulation

Planet opaque disk of radius r/Rs

Transit: every two minutes, the planet is centered at a given position in its orbit (aorb/Rs and i) calculate the integrated flux by summing the intensity in all the pixels

CoRoT-Exo-2 systemCoRoT-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

77 transits

ModelModel

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*

Time (h)

Res

idua

ls

32nd transit

4th transit

Spot modelSpot 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.

0.665 Ic 0.5 R0.5 Rpp(R,I)

4th transit

Spot temporal evolutionSpot temporal evolution

Spot lifetime: 30 + 11 days

Radius

1-Intensity

1exp

1exp

o

e

e

o

KTh

KTh

I

I

Teff=5625 K

Intensity:0.60+0.13 Ic

Temperature:5010+240 K

Radius:0.46+0.14 Rp

-85o 125o

Preferred longitudesPreferred longitudes

Spot numberSpot number

Average spot number = 7

Area covered by spotsArea 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

2 Rp

x1

x2

Spot area coverageSpot area coverageFitted spot radius and intensity:Area = 18.5 %

Fitted only spot radius:Area = 10 - 40 %

Spot mean characteristicsSpot mean characteristics

“Planet radius” = 1.544 RJup (little larger than estimated without considering stellar spots)

Radius 0.46+0.14 Rp (5.0+1.5)x104 km

Intensity – temperature

0.60+0.13 Ic 5010+240 K

Preferred longitudes -66o, 114o

# spots – area coverage

7+1 18 - 20 %

Lifetime 31+11 days no periodicity

Future workFuture workResults 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)

Merci !Merci !

LifetimeLifetime

32+11 days

29+11 days