Search for planetary candidates within the OGLE stars

1. Search for planetary candidates within the OGLE stars Adriana V. R. Silva & Patrícia C. Cruz CRAAM/Mackenzie COROT 2005 - 05/11/2005

2. 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 up • Silva & Cruz – Astrophysical Journal Letters, 637, 2006 (astro-ph/0505281)

3. Planet definition • Based on the object’s mass According 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).

5. 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.

6. Extra-solar Planets Encyclopedia • www.obspm.fr/encycl/encycl.html • 169 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.

7. Radial velocity shifts Planetary mass determined:

8. Venus transit – 8 June 2004

9. Transits

10. HD209458 In 2000, confirmation that the radial velocity measurements were indeed due to an orbiting planet.

11. 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.

12. 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).

13. Transit simulation

14. 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/Rsandi) and the total flux is calculated;

15. Transit Simulation

16. r aorb i 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.

17. aorb 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;

18. 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.

19. OGLE 132 OGLE 122 test OGLE 56 OGLE 111 OGLE 113 HD209458 TrES-1 OGLE 10

20. Model test results

21. Fit Parameters

22. Equations • 4 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:

23. Model parameters

24. 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

25. Model parameters 0.7<<2.3 R2<1.5 RJ

27. Comparison with other results • 100% 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.

28. 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 (RM0.8), 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 M0.1 Msun and sizes similar to Jupiter’s.

29. CoRoT • Method can be easily applied to CoRoT observations of transits.