Search for planetary candidates within

the OGLE stars

Adriana V. R. Silva & Patrícia C. CruzCRAAM/Mackenzie

COROT 2005 - 05/11/2005

Summary

Method to distinguish between planetary and stellar companions;

Observed transits in OGLE data:– 177 stars;

Model:– Orbital parameters: P; r/Rs, a/Rs, i– Kepler’s 3rd law + mass-radius relation for MS stars

Results tested on 7 known bonafide planets;28 proposed planetary candidates for

spectroscopic follow upSilva & Cruz – Astrophysical Journal Letters,

637, 2006 (astro-ph/0505281)

Planet definition

Based on the object’s massAccording to the IAU WORKING GROUP

ON EXTRASOLAR PLANETS (WGESP): stars: objects capable of thermonuclear

fusion of hydrogen (>0.075 Msun); Brown dwarf: capable of deuterium

burning (0.013<M<0.075 Msun); Planets: objects with masses below the

deuterium fusion limit (M<13 MJup), that orbit stars or stellar remains (independently of the way in which they formed).

Newton’s gravitation law

Both planet and star orbit their common center-of-mass.

Planet’s gravitational attraction causes a small variation in the star’s light.

The effect will be greater for close in massive planets.

2

*

r

mGMF plan

Extra-solar Planets Encyclopedia

www.obspm.fr/encycl/encycl.html169 planets (until 24/10/2005):

– 145 planetary systems – 18 multiple planetary systems

9 transiting: HD 209458, TrES-1, OGLE 10, 56, 111, 113, 132, HD 189733, HD 149026.

23/2

*

3/1

1

1

)(

sen2

eMM

iM

P

GK

p

p

Planetary massdetermined:

Radial velocity shifts

Venus transit – 8 June 2004

Transits

HD209458

In 2000, confirmation that the radial velocity measurements were indeed due to an orbiting planet.

Planetary detection by transits

Only 9 confirmed planets.Orbits practically perpendicular to the

plane of the sky (i=90o).Radial velocity: planet mass;Transit: planet radius and orbit inclination

angle;Ground based telescopes able to detect

giant planets only. Satellite based observations needed for detection of Earth like planets.

OGLE project

177 planets with “transits”;Only 5 confirmed as planets by radial

velocity measurements (10, 56, 111, 113, 132).OGLE data (Udalski 2002, 2003, 2004)

Published orbital period

Model the data to obtain:– r/Rs (planet radius);

– aorb/Rs (orbital radius – assumed circular orbit);

– i (inclination angle).

Transit simulation

Model

Star white light image of the sun;

Planet dark disk of radius r/Rs;

Transit: at each time interval, the planet is centered at a given position in its orbit (with aorb/Rs and i) and the total flux is calculated;

Transit Simulation

Lightcurve

I/I=(r/Rs)2, larger planets cause bigger dimming in brightness.

For Jupiter 1% decrease Larger orbital radius

(planet further from the star) yield shorter phase interval.

Inclination angle close to 90o (a transit is observed).

Smaller angles, shorter phase interval;

Grazing transits for i<80o.

r

aorb

i

Orbit

Circular orbits; Period from OGLE project; Perform a search in parameter space for the

best values of r/Rs, aorb/Rs, and i (minimum 2). Error estimate of the model parameters from

1000 Monte Carlo simulation, taken from only those within 1 sigma uncertainty of the data;

aorb

Test of the model

7 known planets: HD 209458, TrES-1, OGLE-TR-10, 56, 111, 113, and 132

OGLE-TR-122 which companion is a brown dwarf with M=0.092 Msun and R=0.12 Rsun (Pont et al. 2005)

Synthetic lightcurve with random noise added.

M1 (Msun) M2 (Msun) R2 (RJ) Semi-axis AU)

angle

Input 4.00 0.32 3.9 0.075 84

Output

3.75 0.29 3.6 0.074 85.3

OGLE 10

OGLE 56 OGLE 111 OGLE 113

OGLE 132

HD209458

OGLE 122 test

TrES-1

Model test results

Fit

Para

mete

rs

3

2

2

31

21 4

sR

a

GPR

MM

Equations4 unknowns: M1, R1, M2, and R2

Kepler’s 3rd law:

Transit depth I/I:

Mass-radius relationship for MS stars (Allen Astrophysical Quantities, Cox 2000) for both primary and secondary:

31

221

23

4

)(

R

MMGP

R

a

s

8.0

11

SunSun M

M

R

R

1

2

R

R

R

R

s

p

8.0

22

SunSun M

M

R

R

Model para

mete

rs

Planetary candidates selection

Density: – Densities < 0.7 to rule out big stars (O, B, A): 1-

2% dimming due to 0.3-0.5 Msun companions:

– Densities > 2.3 maybe due to M dwarfs or binary systems.

Radius of the secondary:

28 candidates

sun 3.27.0

JRR 5.12

3

2

2

31

21 4

sR

a

GPR

MM

Model para

mete

rs

0.7<<2.3R2<1.5 RJ

Comparison with other results100% agreement with:

– Elipsoidal variation: periodic modulation in brightness due to tidal effects between the two stars (Drake 2003, Sirko & Paczynski 2003)

– Low resolution radial velocity obs. (Dreizler et al. 2002, Konacki et al. 2003)

– Giants: espectroscopic study in IR (Gallardo et al. (2005)

6 stars (OGLE-49, 151, 159, 165, 169, 170) failed the criterion of Tingley & Sackett (2005) of >1.

Conclusions From the transit observation of a dim object in

front of the main star, one obtains: – Ratio of the companion to the main star radii: r/Rs;– Orbital radius (circular) in units of stellar radius: aorb/Rs;– Orbital inclination angle, i, and period, P.

Combining Kepler’s 3rd law, a mass-radius relation (RM0.8), and the transit depth infer the mass and radius of the primary and secondary objects.

Model was tested successfully on 7 known planets.

28 planetary candidates: density between 0.7 and 2.3 solar density and secondary radius < 1.5 RJ.

Method does not work for brown dwarfs with M0.1 Msun and sizes similar to Jupiter’s.

CoRoT

Method can be easily applied to CoRoT observations of transits.