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Search for planetary candidates within the OGLE stars Adriana V. R. Silva & Patrícia C. Cruz CRAAM/Mackenzie COROT 2005 - 05/11/2005
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Summary Method to distinguish between planetary and stellar companions; Observed transits in OGLE data: –177 stars; Model: –Orbital parameters: P; r/R s, a/R s, i –Kepler’s 3 rd 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)
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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 M sun ); Brown dwarf: capable of deuterium burning (0.013<M<0.075 M sun ); Planets: objects with masses below the deuterium fusion limit (M<13 M Jup ), that orbit stars or stellar remains (independently of the way in which they formed).
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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.
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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.
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Planetary mass determined: Radial velocity shifts
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Venus transit – 8 June 2004
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Transits
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HD209458 In 2000, confirmation that the radial velocity measurements were indeed due to an orbiting planet.
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Planetary detection by transits Only 9 confirmed planets. Orbits practically perpendicular to the plane of the sky (i=90 o ). 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.
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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/R s (planet radius); –a orb /R s (orbital radius – assumed circular orbit); –i (inclination angle).
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Transit simulation
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Model Star white light image of the sun; Planet dark disk of radius r/R s ; Transit: at each time interval, the planet is centered at a given position in its orbit (with a orb /R s and i) and the total flux is calculated;
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Transit Simulation
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Lightcurve I/I=(r/R s ) 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 90 o (a transit is observed). Smaller angles, shorter phase interval; Grazing transits for i<80 o. r a orb i
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Orbit Circular orbits; Period from OGLE project; Perform a search in parameter space for the best values of r/R s, a orb /R s, 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; a orb
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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 M sun and R=0.12 R sun (Pont et al. 2005) Synthetic lightcurve with random noise added. M 1 (M sun )M 2 (M sun )R 2 (R J )Semi-axis AU)angle Input4.000.323.90.07584 Output3.750.293.60.07485.3
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OGLE 10 OGLE 56OGLE 111OGLE 113 OGLE 132 HD209458 OGLE 122test TrES-1
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Model test results
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Fit Parameters
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Equations 4 unknowns: M 1, R 1, M 2, and R 2 Kepler’s 3 rd law: Transit depth I/I: Mass-radius relationship for MS stars (Allen Astrophysical Quantities, Cox 2000) for both primary and secondary:
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Model parameters
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Planetary candidates selection Density: –Densities < 0.7 to rule out big stars (O, B, A): 1-2% dimming due to 0.3-0.5 M sun companions: –Densities > 2.3 maybe due to M dwarfs or binary systems. Radius of the secondary: 28 candidates
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Model parameters 0.7< <2.3 R 2 <1.5 R J
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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.
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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/R s ; –Orbital radius (circular) in units of stellar radius: a orb /R s ; –Orbital inclination angle, i, and period, P. Combining Kepler’s 3 rd law, a mass-radius relation (R M 0.8 ), 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 R J. Method does not work for brown dwarfs with M 0.1 M sun and sizes similar to Jupiter’s.
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CoRoT Method can be easily applied to CoRoT observations of transits.
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